I BULLETIN OF THE 



the distinguished naturalists whose names are quoted above. It must bo 

 admitted that honest differences of opinion may exist in regard to the 

 specific limits of almost any species of animal ; in this, as in other cases, 

 . I can only give utterance to my own personal opinion, based upon the 

 material at my command. I have, in another publication, stated that I 

 have found constant, though not extreme, differences between this species 

 and T. vilrea, and, as no transition from the one to the other has yet been 

 shown, I feel justified in considering these differences as of specific value. 

 They were partly pointed out by M. de Pourtales in his original descrip- 

 tion ; and after a careful examination of many hundred specimens, and a 

 critical comparison of them with a large series of T. vilrea, I have not been 

 able to detect any inconstancy in the form of the loop in each species. 

 While the other characters arc more variable, yet even those show no 

 more approach to each other than may usually be observed in two closely 

 allied species. 



The following comparative diagnoses will serve to point out these differ- 

 ences : — 



T. cubensis has the. margin of the valves laterally flexuous, varying to 

 some extent in degree of flexuosity, with age. This diagnosis, however, 

 refers to adult shells, in which a certain amount of flexuosity is always 

 present. The convexity being in a homial direction, the margin of the 

 hamuli valve is excavated on each side, giving the valve a subquadrangular 

 aspect. The valves are usually rather inflated, giving the shell a tumid 

 aspect. The hinge teeth are stout and thick, the deltidium moderate ; 

 foramen rather large. The shell is widest near the anterior margin of the 

 valves, the cardinal border is strongly arched ; the cardinal process is 

 stout, blunt, broad, rounded and much recurved. The cardinal plate is 

 divided ; no shelly matter extending between the apophysal ridges. The 

 shelly plates on each side of these ridges, extending to the dental ridges, 

 are deeply concave, with the anterior border somewhat produced ami 

 rounded. The crura are short and blunt. The anterior part of the loop 

 is characteristic and peculiar. It is strongly squarely convex in the mid- 

 dle, and a deep narrow gutter extends on each side of this convexity and 

 is produced at each side into a point. Between these points and the 

 median convexity on each side is a deep slit or fissure. The anterior end 

 of the convexity is much produced, blunt, and square. It terminates be- 

 hind in a slight sinus or indentation. The apex of the haemal valve is 

 much incurved. 



T.vitrea has the lateral margins of the valves almost rectilinear, if there 

 be any flexuosity the direction of the convexity is neural. Hence the 

 outline of the hannal valve is rounded ovate. The valves are more or less 

 compressed, and there are frequently indications of a broad median ridge, 



