I would suggest to consult the following references:
Capapé, C. and M. Desoutter 1979. Nouvelle description de Aetomylaeus nichofi (Bloch et Schneider, 1801) (Pisces, Myliobatidae). Premières observations biologiques. Cahiers de l'Indo-Pacifique v. 4: 305-322.
Ruocco, N. L. , L. O. Lucifora, J. M. Díaz de Astarloa, E. Mabragaña, and S. M. Delpiani 2012. Morphology and DNA barcoding reveal a new species of eagle ray from the southwestern Atlantic: Myliobatis ridens sp. nov. (Chondrichthyes: Myliobatiformes: Myliobatidae). Zoological Studies v. 51 (no. 6): 862-873.
White, W. T. 2014. A revised generic arrangement for the eagle ray family Myliobatidae, with definitions for the valid genera. Zootaxa 3860 (no. 2): 149-166.
White, W. T. , J. Kawauchi, S. Corrigan, E. Rochel and G. J. P. Naylor 2015. Redescrition of the eagle rays Myliobatis hamlyni Ogilby, 1911 and M. tobijei Bleeker, 1854 (Myliobatiformes: Myliobatidae) from the east Indo-West Pacific. Zootaxa 3948 (no. 3): 521-528.
White, W. T. , P. R. Last and L. Baje 2015. Aetomylaeus caeruleofasciatus, a new species of eagle ray (Myliobatiformes: Myliobatidae) from northern Australia and New Guinea. Ichthyological Research: [1-16].
White, W. T. , P. R. Last, G. J. P. Naylor, K. Jensen and J. N. Caira 2010. Clarification of Aetobatus ocellatus (Kuhl, 1823) as a valid species, and a comparison with Aetobatus narinari (Euphrasen, 1790) (Rajiformes: Myliobatidae). In: Descriptions of new sharks and rays from Borneo. CSIRO Marine and Atmospheric Research Paper No. 032: 141-164.
White, W. T. and A. B. M. Moore 2013. Redescription of Aetobatus flagellum (Bloch & Schneider, 1801), an endangered eagle ray (Myliobatoidea: Myliobatidae) from the Indo-West Pacific. Zootaxa 3752 (no. 1): 199-213.
Hay un monográfico reciente en Palaeontos nº 24 que hace una revisión de todas las morfologías actuales. También revisan especies fósiles. Resulta que una misma especie tiene más de una morfología inicialmente atribuida en fósiles a varias especies.
Hovestadt D.C. & Hovestadt-Euler M., 2013, Generic assessment and reallocation of Cenozoic Myliobatins based on new information of tooth, tooth plate and caudal spine morphology of extant taxa. ISSN: 1377-4654
SCHWARTZ, F.J. (2005). Tail spine characteristics of Stingrays (Order Myliobatiformes) found in the northeast Atlantic, Mediterranean, and Black Seas. Electronic Journal of Ichthyology, July, 1: 1- 9
http://ichthyology.tau.ac.il/2005/Stingray.pdf
GRAVENDEEL, R., VAN NEER, W., BRINKHUIZEN, D. (2002). An Identification Key for Dermal Denticles of Rajidae from the North Sea. International Journal of Osteoarchaeology, 12 (6): 420-441