50 THE NAUTILUS. 



S. quadratus Walker. Only a single example shows any trace 

 of the sculpture, which though eroded above, is distinctly lirate 

 below. Apical whorl not everted, rounded and shouldered 

 above, not constricted by the suture. 



S. sargenti Pilsbry. Variable as to the elevation of the apical 

 whorl, (which is usually rather blunt) ; some amount of ever- 

 sion and constriction by the suture. Sculpture, distinctly 

 spirally punctate above, lirate below. 



S. strengii P. and W. This species is remarkable free from 

 erosion, probably on account of the depressed apical whorls, 

 which are planorboid, flattened above, with a well impressed 

 vertical suture. Apical whorl flatly rounded, not everted, 

 quite rapidly increasing. Apex somewhat immersed. Sculp- 

 ture very minutely wrinkled and spirally punctate, hardly dis- 

 cernible with 100 diameters, no lirse. 



S. subglobosus Say. Apical whorl prominent, rather small, 

 slightly everted, rounded, but not greatly constricted by the 

 suture, obliquely flattened above. Sculpture, at first wrinkled 

 or malleated, then more or less punctate on the upper surface, 

 which rapidly becomes punctate-lirate, lirate below. 



S. substriatus Walker. Apical whorl prominent, elevated, 

 somewhat everted and obliquely flattened above, rounded, but 

 not greatly constricted by the suture below. Sculpture, more 

 or less irregularly wrinkled and malleated on the first half of 

 the whorl, but becoming obsolete on the second half, no lira?. 



S. trothis Doherty. Apical whorl bluntly elevated, everted 

 and obliquely flattened above, not greatly constricted by the 

 well impressed suture, rapidly enlarging. Apex not depressed 

 below the surrounding whorl. Sculpture, quite well wrinkled 

 at first, then spirally punctate above and obsoletely lirate below. 



S. virginicus Walker. Quite similar to pennsylvanicus, to 

 which it is allied, but the apical whorl is rather higher, rounded 

 and more constricted by the suture, being more closely coiled. 

 Sculpture, substantially the same in both. 



walkerianus Aldrich. Apical whorl much elevated, more 

 so than in any other species, except wheeleri, closely coiled, 

 very convex and greatly constricted by the suture, everted and 

 obliquely flattened above. Sculpture, strongly wrinkled at the 

 tip, then spirally punctate-lirate. 



