INVERTEBRATE PAL2EONTOLOGY. 235 



least an Indian species referred by him to the same, to have the hinge of a 

 Pholadomya : and from his remarks one would almosl think thai I had either 

 founded the genus Liopistha on that species, or, a1 least, that I had included 

 it in proposing this genus. The fact is, however, that my type-species was, 

 as already stated, Card'mm elegantulum, Roerner ; and I did not even allude 

 to Pholadomya caudata in any way in connection with Liopistha. 



Nevertheless, from Dr. Stoliczka's figures of the exterior, and the hinge 

 of t he right valve of the Indian shell that he refers to P. caudata, I am inclined 

 to believe that it will be found to be a Liopistha and not a Pholadomya, not- 

 withstanding bis very positive assertion to the contrary. At any rate, it 

 agrees exactly in thinness and general form, and has the same granular and 

 costate surface: while the flattened cardinal tooth shown in his figure of the 

 right valve corresponds close?)/ to the character of the posterior cardinal 

 tooth in Liopistha and Cymella, excepting that it is placed slightly farther 

 forward. Now, if we were to break out the very delicate anterior cardinal 

 tooth of a right valve of a Liopistha, its agreement with Dr. Stoliczka's figure 

 would l)e exact in almost every respect. Hence, I suspect that the Indian 

 shell figured by him as Pholadomya caudata is really a Liopistha, and that 

 the right valve figured by him to show the hinge, had lost the small anterior 

 cardinal tooth by some accident.* Of course, however, this may or may not 

 be so. without in any way affecting the question in regard to Liopistha being 

 clearly and entirely distinct from Pholadomya, as any one may at once see 

 by reference to our cuts of the hinge of the former. 



On the other hand. Dr. Stoliczka speaks of Cymella as a dubious sort of 

 genus, which he seems to think scarcely distinct from Poromya. So far as 

 regards its relations to the Indian shells referred by him to Poromya, I can 

 agree with him that Cymella is not more than subgenerically distinct from 

 the same: but, for the reasons already stated, I must differ with him, and 

 maintain that both the Indian species and the typical forms of Cymella, as 

 well as Liopistha, are generically distinct from the true Poromya. 



So far as I am at this time informed, the genus Liopistha, including the 

 subgenera, is confined to the Cretaceous rocks. It includes L. elegantula 

 (= Cardium elegantulum, Roerner), L. protexta, Conrad, L. rostrata, Meek, 



* As an illustration of this, I would refer to Mr. Conrad's figure of the hinge of the right valve of 

 Cymella, as given iu the, supplement of the North Carolina Report, which figure was evidently drawr. 

 from a specimen that had met with precisely this very accident, as may be seen by comparing his figure 

 with our cut i Fig. »'ti i of the hinge of the right valve of the same species. 



