Venus stimpsoiii, GonlJ. 135 



bifid, as also is tlie median of the left; whereas in many of 

 the adult Chione the teeth are entire or only feebly grooved. 

 Specifically Venus stiwpsoni m^y be described as follows : — 

 Shell large, solid, triangularly-ovate, more attenuated poste- 

 riorly than other species, the postero-dorsal slope being 

 flattened and elongated so as to meet the postero-ventral 

 slope in an angle wliicii approximately subtends the median 

 transverse diameter of the shell. The anterior side is evenly 

 rounded and somewhat compressed. The specimen measui*es 

 a little over o^ inches in length by 2f in height ; more 

 accui-ately it is 9 cent, long by 7-3 cent, high across the 

 middle of the shell. 



The sculpture consists of numerous low concentric lamellae 

 which are very close-set on the two sides and near the ventral 

 border of the valves. On the central part of each valve the 

 spaces between the lamellaj are striated concentrically but 

 ii-regnlarly, and are also crossed by faint radiating lines. 

 The valves are somewhat compressed, so that tlie width from 

 centre to centre is less than in V. mercenaria and the shell is 

 consequently less ventricose. 



The internal characters are like those of V. mercenaria, 

 but the rugose areas of the hinge are narrower and less 

 pronounced. The pallial sinus is rather smaller, and the 

 muscular scars rather larger than in the type species. The 

 crenulated inner margin of ihe valves is very narrow and the 

 crenulations on the lunular margin are faint. Still the 

 margins are not '^simple "" as stated by Mr. Gould ; possibly 

 his specimen was somewhat worn. 



The Mercenaria section of Venus is almost entirely 

 American, V. siimpsoni being the only species yet recognized 

 outside American waters, though some Australasian species, 

 such as V. yatei, Gray, and V. alala, Reeve, come very near 

 to it. 



There are two species on the east coast of America, 

 V. mercenaria, Linn., and V. campechiensis, Gmelin ( = 

 V. mortoni, Conrad). Two also occur on the west coast, 

 viz., V. kennicotd, Dall, and V. apodema, Dall, but both are 

 very rare. V. stimpsoni is probably most nearly allied to 

 V. kennicolti, for Dr. Dall describes this latter species as 

 being yellowish white in colour and closely lamellose over 

 the whole surface ; he also says " the rugose area of the 

 hinge is more narrow and delicate than in the Atlantic 

 species, but this area is still further diminished in the 

 Japanese V. stimpsoni (Gould), the only exotic species of the 

 group." 



