ACADEMY OF SCIENCES. 99 



^ 1. Only three whorls visible above. 



28 subcrenatus Cpr. Wh. 6, rounded, growth lines strong, often giving 

 the outline a crenated appearance, mouth slightly narrowed below ; diam. *1.05, 

 alt. *0.36. 



Q? gluhmtus Say. Wh. 5, obsoletely rugose, round' d, mouth oblique, sub- 

 oval, several obtuse angles in outline ; diam. 0.80, alt. 0.20. 



Specimens, common inland, closely resemble this, but may be mbcrenatus. 



29 tumens Cpr. Wh. 4-.5, nearly smooth, swollen, beneath more or less  

 angled, narrowing the mouth to an obtuse triangle ; diam. *0.G3. alt. *n.27. 



30 H or n i i Tryon. Wh. 5, uniformly rounded, smooth, ends of lip nearly 

 meeting, mouth suborbicular ; diam. *0.84, alt. *0.28. 



Q? 31. Oregonensis Tryon. Wh. 3, but two visible above, rapidly 

 expanding; diam. *0.36, alt. *0.1G. (Probably young of Helisoma Binneyi.) 

 I 2. Four to five whorls visible above. 



Q. 32 gracilentus Gld. Wh. 4, the same on both sides, rounded, the 

 last obtusely carinated at middle, mouth oblique oval, wider than high ; diam. 

 *0.o0, alt. 0. 2. 



Subgenus BELJSOMA Swains. Shell with last whorl much higher than 

 spire, mouth usually higher than wide, sub-angled below, ear-shaped. 



33 ammo n Gld. Wb. 4, but 2% visible above, nearly smooth, last whorl 

 and mouth much higher than wide, spire deeply sunken and small ; diam. *0.25- 

 1.05, alt. *0.60-0.86. 



Var. ? Traskii Lea. Wh. 5, the two last 6f nearly equal height, less 

 narrowed below ; diam. *1.05, alt. *0.86. 



34 c c i d e n t a 1 i s Cp. n. s. Wh. 5-6, nearly all visible above, much nar- 

 rowed and sub-angled below, nearly smooth, mouth little higher than wide, diam. 

 0.80-1.00, alt. 0.50-0.70. 



N. B. This has been called trivohis and tenuis, but differs from both in the 

 much greater narrowing of the whorls below (approaching ammoii), and from 

 all, in the larger number visible above in large specimens. From amnion, also, 

 in lower body-whorl. Binney's fig. 193 represents a form of it. Its range 

 extends from Washington Terr, to Kern Lake, and along thcv^oast to San Jos^. 



Q. 35 Binneyi Tryon, Amer. Jour. Conch. Ill, 1867; corpulentus Hald. 

 1844, Gould, 1852, W. G. Binney, Land & Freshwater Sliells, II, 1865, 115, 

 fig. 191, 192, not of Say (?) Mouth little higher than wide ; diam. *0.90, alt. 

 *p.65. 



Tryon gives no diagnostic characters, but the figures look like a small north- 

 ern variety of aminon, not mature, and nearest to var. Traskii which is found 

 at Stockton, etc. 



Subgenus G YRA UL US Agassiz. Shell small, whorls rounded, some- 

 times flattened below. 

 36 verraicularis Gld. Wh. 3-4, cylindrical, or oval, upper surface 

 nearly plane, lower more concave ; diam. *0.20, alt. *0.06-0.07. 



Q. 37 parvus Say. Wh. 4, section sub-angled at periphery, both sur- 

 faces about equally concave ; diam. *0.20, alt. 0:67. 



