476 Mr. A. J. Jukes-Browne on the Shells 



Fischer (1887) and by Dull in 1889, but in 1902 the latter 

 transferred it to the Venerida?, and placed it after Gemma in 

 his " Synopsis of the Veneridoe," giving at the same time a 

 full and accurate description of the shell*. 



Parastarte resembles Gemma in most respects, but differs 

 in two particulars : first, the pallial line is hardly sinuated, 

 but only slightly inflected ; secondly, the left valve has only 

 two- divergent teeth, separated by a triangular space to 

 receive the strong central tooth of the right valve ; these two 

 teeth are clearly anterior and median, so that it is the poste- 

 rior cardinal which is missing in the left valve, crowded out 

 by the thickness of the two median teeth and the narrowness 

 of the triangular hinge-plate. 



We have seen that in Gemma this left posterior tooth is 

 reduced to an inconspicuous ridge, and, as a matter of fact, it is 

 often obsolete in the variety G. purpurea, so that, as Dr. Dall 

 himself admits, he at one time actually referred this variety 

 of Gemma to Parastarte. It, therefore, we consider Par- 

 astarte as a laterally compressed Gemma, we can readily 

 understand how this tooth has been eliminated. 



I am consequently quite of Dr. Dall's opinion that this 

 shell is closely related to Gemma, but 1 do not consider it 

 entitled to rank as more than a subgenus of Gemma. It 

 exhibits similar ridges and grooves on the dorsal margins of 

 its valves, and it is to be noticed that Dr. Dall has never 

 ventured to call them lateral teeth, either in his " Synopsis of 

 the Veneridse " (1902) or in his 'Monograph on the Tertiary 

 Fossils of Florida ' (1903). On the contrary, he describes 

 the dorsal margins of Parastarte as " feebly grooved to 

 receive the edges of the opposite valve." Again, in his 

 article on Gemma, above mentioned, he writes : — " The 

 nearest relative of Gemma is the genus Parastarte^ Conrad, 

 which differs chiefly by its obsolete pallial sinus and the 

 absence of the left posterior cardinal tooth. Concurrently 

 the lateral grooving of the margins is less distinct.'" 

 Nothing whatever is said about the corresponding ridges 

 which in Gemma he imagined to be lateral teeth ! If they 

 are such in Gemma, why are they not in its "nearest 

 relative " ? The only logical answer is that no lateral teeth 

 exist in either shell. 



In view of the facts and considerations above mentioned, 

 and of the close relationship between Parastarte and Gemma, 

 it seems desirable to describe the genus once more, and in 

 such a manner as to discriminate between the typical form 



* Proc. U.S. Nat. Museum, vol. xxvi. p. 365 (1902). 



