THE ANNALS 



AND 



MAGAZINE OF NATURAL HISTORY. 



[SECOND SERIES.] 

 No. 44. AUGUST 1851. 



VIII. — On the Hinge of the Fossil Genus Platymya, Agassiz ; 

 with the description of a new species. By J. Lycett, Esq.* 



M. Agassiz proposed to constitute his genus Platymya with 

 certain flattened and gaping bivalve shells whose figui-e differs 

 sufficiently from that of other genera of fossil Myadse, and he 

 characterized with precision the external features of the group ; 

 but as the hinge remained unknown to him, the genus could not 

 be considered as established. Subsequently M. D^Orbigny, from 

 a consideration of several other species which he described in the 

 ' Paleontologie Fran9aise/ believing that he had discovered in cer- 

 tain of their moulds impressions of an internal spoon-shaped pro- 

 cess, and likewise of the rib which abuts against it, concluded 

 that some of the species at least were true Anatinas, and therefore 

 designated them as such. On the other hand, M. Agassiz f, 

 whilst admitting the full importance of the characters noticed 

 by M. D'Orbigny, and the possibility that in consequence Pla- 

 tymya may be reduced to the rank of a subgenus only, states 

 his impression that nevertheless it may be a good genus, and 

 directs attention to an important distinction between the two 

 forms, viz. that in the Anatinas the anterior region is the most 

 produced, but in Platymya it is the posterior which is most pro- 

 minent. M. Agassiz therefore refused to abandon his genus Pla- 

 tymya, and reunited the six Anatinas of M. D'Orbigny to his 

 own as additional species of Platymya. Platymya is exemplified 

 in the ' Etudes Critiques ' by six species only ; the number of in- 

 dividuals in each species is stated to be but very few, and that 

 the form altogether had not previously been noticed by palaeon- 

 tologists. All of the species pertain to the Cretaceous system of 

 rocks with two exceptions, one belonging to the upper, and the 



* Read to the Cotswold Naturalists' Club, June 24, 1851. 

 t Etudes Critiques sur les Mollusques fossiles, Mves, Introduction,}), xvi. 

 Ann. ^- Mag. N. Hist. Ser. 2. Vol. viii. " 6 



