DALL : ON THE GENUS GEMMA, DESHAYES. 24I 



As regards the name, while the repetition of Gemma is objectionable 

 from an aesthetic standpoint, I hold that this is insufficient to cause its 

 rejection. Such a rule would upset hundreds of genera in current use, 

 given by Linne, Lamarck, Cuvier and other most distinguished and 

 classical authorities and in no way benefit science. The British 

 Association paragraph should be accepted as a useful suggestion, but 

 cannot be erected into an ex post facto law. From Deshayes' original 

 manuscripts in my possession I know that his genus was originally 

 written Geinmula, but how it came to be printed Gemma is now past 

 finding out, 



The original Ve/nis gemma of Totten included two forms, of which 

 the extremes are very well marked; though the connecting variations 

 are so numerous that they can hardly be regarded as of higher, rank 

 than subspecies. One of these is the form which extends from Long 

 Island Sound to Labrador, and which for convenience we may regard 

 as the subspecies Tottenii of Stimpson. The other extends from 

 Jupiter Inlet, south-east Florida, to Cape Cod. In the vicinity of 

 Cape Cod and around to New York Bay these forms are found more 

 or less intermingled and intergraded. Either of them may vary from 

 purple to pale straw colour. Lea's Cyrena purpurea is a young speci- 

 men of the southern form. Prime's Venus mafihaifa/iensis is a white, 

 compressed variety of the same. The specimens usually named 

 vianhattane?isis are only white specimens of either subspecies. A 

 manuscript note of Stimpson's states that Totten's cabinet specimens 

 were purple like 2i^w\\. purpurea, but his original description evidently 

 included both, and his figure is the oval Tottenii variety. 



GEMMA GEMMA (Totten). 

 Gemma gemma subsp. tottenii Stm. 



Trajis. Wagner Inst., vol. 3, pt. 4, pi. 24, figs, i, 3, 1898. 



This shell is oval, rather compressed, with a faintly marked lanceo- 

 late lunule, flattish often irregular or obsolete concentric waves, 

 glistening surface and generally eroded beaks. The pallial sinus 

 averages higher and more acute than in the southern form but is 

 variable. The dentition is exactly the same. The colours vary 

 through the same range. The ligament is a little longer proportion- 

 ately than in the southern form. 



Gemma gemma subsp. purpurea Lea. 



Trans. Wagner Inst., vol. 3, pt. 4, pi. 24, figs. 2, 4, 4b, 1898. 



This shell is rounded triangular, inflated, with more prominent 

 beaks, wider lunule and shorter ligament. The concentric sculpture 

 is in smaller waves, but they are much more prominent, regular and 

 conspicuous. I have seen none of this shape with obsolete waves as 



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