JDKES-BROAVNK : SYTNOPSIS OF THE VENERID.15. 87 



reasons for regarding Parastarte as a sub-genus, I need only here 

 quote the definitions there printed. It is a small group of small 

 American shells which seeras to stand by itself, though, by the 

 characters of the hinge and the crenulation of the margins, it 

 resembles Cliione more than any other. 



Shell small, oval or sub-trigonal, smooth or concentrically striated. 

 Lunule large, superfi.cially defined. No escutcheon. Hinge-plate 

 short. Teeth widely divergent, the left posterior inconspicnous or 

 obsolete, but, when present, parallel to the nymph ; left median and 

 right posterior bifid, all the rest entire. Jliglit postero-dorsal and left 

 antero-dorsal margins grooved to receive ridges on the opposite margins. 

 Ventral margins finely crenulated. 



Gemma, s.s. Type, Venics ffemma, Totten. 



Shell oval, striate. Three teeth in each valve. Marginal grooves 

 long and deep. Pallial sinus generally rounded, ascending. 



Sub-^enus. 

 Parastarte, Dall. Shell thick, smooth, equilateral, and sub- 

 trigonal. Tliree teeth in the right valve and only two in the left. 

 Marginal giooves narrow. Pallial line only slightly inflected. 



Genus CrPKiMERiA, Conrad, 1864. 



Fossil shells of Cretaceous age, and represented by one small species 

 in the Eocene of the Paris Basin. 



Shell more or less orbicular, smooth or concentrically striated, 

 Umbones small. Lunule superficial and feebly defined. No escutcheon. 

 Hinge-plate prolonged anteriorly to form a concave space. Teeth 

 widely divergent, the right posterior being so broadly bifid that its 

 components form two separate teeth, while the median and anterior 

 are directed forward. Left median thick and sometimes bifid. 



Ci/pn'meria, s.s. Type, Cytherea excavata, ^Morton. 



Shell sub-orbicular, compressed. Left median tooth thick, triangular 

 and bifid ; left posterior long and nearly parallel to the nymph. Pallial 

 line with a very slight inflection. 



Ci/clorisma, Dall, 1902. Type, C. earolineiisi's, Conrad. 



Shell oval or sub-orbicular, convex. Left median tooth entire, left 

 posterior short and crossing the plate obliquely. Pallial sinus fairly 

 deep, ascending and subangular. 



Genus Makcia, H. & A. Adams, 1857. 



This genus and its separation from Tapes have been fully discussed 

 in a previous paper.' Tiie name was proposed by the Messrs. Adams 

 in their Genera of Recent Mollusca in 1857 for a group of shells which 

 they regarded as a sub-genus of Chione. By Bijmer, however, these 

 species were included in his Ilemitapes and Katehjsia groups, the 

 former being regarded as a section of Tapes; and in 1887 Fischer 

 recognized Marcia, as well as Ilemitapes and Katehjsia, placing them 



' Proc. Malac. Soc, vol. viii, p. 233, 1909. 



