Holotype and isotypes are separately mounted specimens of the same accession. Holotype is that specimen from these sheets which is marked(designated) so  in the protolouge. All the other specimens with same collection number are treated as isotypes.

In some earlier cases where more than one specimen are mounted on the same sheet and that sheet forms the Holotype of a taxon, usually  one of the specimen is designated as holotype.  (Some thing like specimen on the left or specimen in flowering or so.)

Dear Mosyakin

It was a case observed in previously described taxon with clear cut indication of type.

And the sheet bears two original labels... and two different Barrowden numbers...

And I understand that a holotype may be a single specimen comprising of several small individuals mounted as a single preparation...

Obviously... if I am talking about holotype and isotope. .. then definitely, the details and collection number on both the labels are same. It differs only in accession nhmber/ barca de. .

And exactly... my point was to confirm the doubt regarding further typifiying the taxon, but what if the both the individuals are of same taxon...

Do you think a single herbarium voucher will be a holotype as well as isotope for a single taxon

Thank you 

Danish husain

 Dear SM

The protologue dates of time when the concept of holotype to be one specific specimen was not evolved in the Code (ICN) and obviously barcoding is also of recent time only.... Obviously the specimen was not designated as holotype or isotope by the authorities of the species.... some other fellow after revising the taxon stated it to be as holotype and isotype.... 

Dear Danish,

See the interesting examples given below in addition to...'a holotype may be a single specimen comprising of several small individuals mounted as a single preparation...' 

• 8.3 A specimen may be mounted as more than one preparation, as long as the parts are clearly labelled as being part of that same specimen. Multiple preparations from a single gathering that are not clearly labelled as being part of a single specimen are duplicates2, irrespective of whether the source was one organism or more than one (but see Art. 8.5).

o Ex.2. The holotype specimen of Delissea eleeleensis H. St. John, Christensen 261 (BISH), is mounted as two preparations, a herbarium sheet (BISH No. 519675) bearing the annotation “fl. bottled“ and an inflorescence preserved in alcohol in a jar labelled “Cyanea, Christensen 261“. The annotation indicates that the inflorescence is part of the holotype specimen and not a duplicate, nor is it part of the isotype specimen (BISH No. 519676), which is not labelled as including additional material preserved in a separate preparation.

o Ex.3. The holotype specimen of Johannesteijsmannia magnifica J. Dransf., Dransfield 862 (K), consists of a leaf mounted on five herbarium sheets, an inflorescence and infructescence in a box, and liquid-preserved material in a bottle.

o Ex.4. The holotype of Cephaelis acanthacea Steyerm., Cuatrecasas 16752 (F), consists of a single specimen mounted on two herbarium sheets, labelled “sheet 1“ and “sheet 2“. Although the two sheets have separate herbarium accession numbers, F-1153741 and F-1153742, respectively, the cross-labelling indicates that they constitute a single specimen. A third sheet of Cuatrecasas 16572, F-1153740, is not cross-labelled and is therefore a duplicate.

o Ex.5. The holotype specimen of Eugenia ceibensis Standl., Yuncker & al. 8309, is mounted on a single herbarium sheet at F. A fragment was removed from the specimen subsequent to its designation as holotype and is now conserved at LL. The fragment is mounted on a herbarium sheet along with a photograph of the holotype and is labelled “fragment of type!“. The fragment is no longer part of the holotype specimen because it is not permanently conserved in the same herbarium as the holotype. It has the status of a duplicate, i.e. an isotype.

Narayan has mentioned ' Holotype is that specimen from these sheets which is marked(designated) so in the protolouge'

but see the definition of holotye: • 9.1 A holotype of a name of a species or infraspecific taxon is the one specimen or illustration (but see Art. 40.4) used by the author, or designated by the author as the nomenclatural type. 

Thus even it can be proved that the author of the name did not designate a holotype but USED only a single specimen then that has to be accepted as the Holotype. Holotype is always of a name, NOT a taxon. You said 'holotype and isotype of same taxon' is also not correct. It should be 'holotype and isotype of the name (*******)’.

You have mentioned ‘The protologue dates of time when the concept of holotype to be one specific specimen was not evolved in the Code (ICN) and obviously barcoding is also of recent time only.... Obviously the specimen was not designated as holotype or isotope by the authorities of the species.... some other fellow after revising the taxon stated it to be as holotype and isotype....’

They cannot be holotype and isotype because Barrowden collections in the same sheet bear two different Barrowden numbers...'

In the protologue of the name if both the collections of Barrowden with different collection numbers were indicated as type, then they are definitely syntypes. Even though they are mounted on the same sheet, they constitute syntypes and you MAY designate of these as Lectotype. If the collections are heterogeneous i.e. belonging to two different taxa then lectototypification is a MUST.

If there is a single field number follow the instructions for typification given in the attached publication.

Hope this helps,

Subir.

Dear Dr. Subir 

BARROWDEN NUMBERS was a typological mistake for Barcode number. ..

Sorry for that....

Thank you for coming up with answer...

Subir date is important....

The author of species just indicated type.... not gave a specific specimen. ..

We found one sheet bearing two individuals.... the sheet also bears two original labels.... and two different Barcodes numbers ....

Obviously if this is the case... then the specimens turn out to be syntype. ..

Later on, almost 80 years after this, anonymous stated that  one specimen bearing its own barcode as holotype and other specimen with separate Barcode as isotype....

Both specimens belong to same taxon only....

I studied the situation in light of CODE but could not reach at any conclusion...

And as far as I think.... annotation on specimen as holotype and or isotype is not acceptable. .. since they are syntype. ... any such annotation is faulty and one the taxon needs to be lectotypified. .. what do you say...?

Dear Danish,

I have refined my reply just now. Kindly go through it once again. Can you please upload the protologue and the image of the specimen you have examined?

Dear Danish,

It seems to me that you may not like to disclose the name till you publish it.

In the light of the typographic mistake [BARROWDEN NUMBERS instead of Barcode number], you can deal it in the following way.

If both the specimens attached on the same sheet constitute original material (Art. 9.3), you can use them for typification. If you find the one labeled as holotype by someone exactly matches with the protologue, i.e. it is the only specimen used by the author, then you can accept it as the holotype. If you think that it might be the holotype but not absolutely sure, you can designate it as the lectotype stating: lectotype designated here, if not holotype (see the publication of McNeill), otherwise straightway designate it as the lectotype without stating anything. If you find that the other specimen labeled as isotype is more suitable for typification, you can also designate that as the lectotype (but see Art. 9.12).

Keep in your mind that you are lectotypifying a name not a species or taxon.

Best wishes,

Subir.

Dear Dr. Subir

Apologies for not disclosing. ..

After compiling my manuscript and communicating it, I will disclose it on you....

And thankeep for reminding me that one has to typify the name and not a taxon

Dear Danish ,

No problem. Thanks. I also used to do the same mistake  till Dr. Dan H Nicolson pointed me out that only a name has a type.

Thank You Professor Mosyakin and Dr. Subir for Your Noble Guidance...

Dear Danish,

Sergei is correct. You look for the earlier publications thoroughly also keep in mind the following Article:

• 9.9 The use of a term defined in the Code (Art. 9.1-2 and 9.4-8) as denoting a type, in a sense other than that in which it is so defined, is treated as an error to be corrected (for example, the use of the term lectotype to denote what is in fact a neotype).

o Ex.10. Borssum Waalkes (in Blumea 14: 198. 1966) cited Herb. Linnaeus No. 866.7 (LINN) as the holotype of Sida retusa L. (1763). However, illustrations in Plukenet (Phytographia: t. 9, fig. 2. 1691) and Rumphius (Herb. Amboin. 6: t. 19. 1750) were cited by Linnaeus in the protologue. Therefore the original material of S. retusa comprises three elements (Art. 9.3), and Borssum Waalkes’s use of holotype is an error to be corrected to lectotype.

o Note 6. A misused term may be corrected only if the requirements of Art. 7.10 (for correction to lectotype, neotype, and epitype) are met and Art. 40.6 (for correction to holotype) does not apply.

Dear Dr. Subir and Prof. Mosyakin...

Thank you very much for your noble opinions.... I am looking forward for your valuable remarks.

Regards..

Danish Husain