MARINE MOLLUSC A OP THE UNITED STATES. 6t 



Closely allied to 0. bisuturalis, but is shorter, and spire less 

 acute ; whorls flatter and color darker. 



3. O. DEALBATA, Stimpson. Fig. 116. 



(.Ohemnitzia.) Proc. Bost. Soc. Nat. Hist., iv. 114. 1851. 

 Shell ovate-conic, white, smooth, pellucid ; whorls six, rather 

 convex; aperture ovate, hardly effuse; furnished with a small in- 

 conspicuous fold. 



Length 4, diam. 1.5 mill. 



It is broader than 0. bisuturalis, but has not so sharp an apex, 

 and wants the revolving line. 



Dredged in three fathoms, on a shelly bottom. 



Boston Harbor. 



4. 0. MODESTA, Stimpson. Fig. lit. 



(Chemnitzia.) Proc. Bost. Soc. Nat. Hist., iv. 16. 1851. 

 Shell small, conic, white, smooth ; whorls four, flattened, the 

 last medially sub-angulated ; suture impressed ; aperture unipli- 

 cate, sub-rhomboid. 



Length 3.5, diam. 1.5 mill. 



This species is more angular than 0. bisuturalis, and has no 

 revolving line just below the suture as in that shell. It is very 

 like the British 0. unidentata. It inhabits the Coralline Zone. 



St. George's Banks. 



5. 0. BISUTURALIS, Say. Fig. 118. 



(Turritella.} Journ. Pliilad. Acad., ii. 244. 1821. 

 CTiemnitzia bisuturalis, Stimpson, Shells of N. England, 42. 1851. 

 Jaminea exigua, Couthouy, Bost. Journ. Nat. Hist., ii. 92, t. 2, f. 7. 1838. 

 Odostomia exigua, Gould, Invert. Mass., 1st Edit. 272, f. 77. 1841. 

 Rissoa rupestris, Forbes, Ann. Nat. Hist., ii. 107, t. 2, f. 13. 



Shell ovate-conical, apex rather obtuse, smooth, light-green, 

 epidermis brownish ; whorls five or six, flattened, with an im- 

 pressed line revolving below the suture, giving the appearance of 

 a double suture ; columella with a transverse fold. 



Length 5, diam. 2 mill. 



New England. 



6. 0. TRIFIDA, Totten. Fig. 119. 



(Actceon.) Am. Journ. Science, xxvi. 368, t. 1, f. 4, a, b. 1834. 

 Shell small, elevated, pointed, smooth and glossy ; whorls eight, 

 flat, with about six impressed revolving lines; the one above and 

 the two next below the suture wider and more distinct ; ten or 



