HERMAPHRODITE. 225 



margin, slightly hollowed out. Umbo of growth nearly 

 central. 



Upper Latera, flat, irregularly oval, with an almost 

 rectangular shoulder under the basal angle of the terga ; 

 in area, about one third larger than the largest valve 

 of the lower whorl ; the exact degree of elongation of the 

 oval figure varies a little. Umbo seated a little above 

 the central point. 



Lower Whorl, — 'Rostral Latera, nearly twice as long as 

 broad, lying under the basal margins of the scuta: 

 umbo seated over the rostrum ; opposite end, towards 

 which the valve widens either sensibly or but little, is 

 either square or rounded ; in area, less than any of the 

 other valves, excepting the rostrum ; in breadth, equalling 

 either half or one third of the height of the infra-median 

 latera ; growth, directed chiefly towards the infra-median 

 latera. The freely-projecting umbo is about one sixth 

 part of the entire length of the valve. 



Infra-median Latera, rather larger than the carinal 

 latera; their shape varies from elongated pentagonal 

 with the angles rounded, to oval, with the longer axis 

 directed upwards. The umbo is seated a little above the 

 middle of the basal margin, so that there is some little 

 growth downwards, but the main growth is upwards. 

 The upper point generally stands a little above that of 

 the carinal latera. 



Carinal Latera, flat, less in area than the infra-median 

 latera; basal margin nearly straight; carinal margin 

 slightly hollowed out, terminal margin arched and protu- 

 berant. The umbones of the two valves almost touch each 

 other under the middle of the carina; main growth 

 towards the infra-median latera and upwards ; umbones 

 projecting not above one fifth of the entire length of the 

 valve. 



Peduncle, much flattened, rarely as long as the capi- 

 tulum, with the upper end nearly as wide as it ; the lower 

 end is either blunt, or tapers to a very fine point. The 

 calcareous scales are transversely elongated, and are about 



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