MARINE MOLLUSCA OF THE UNITED STATES. 67 



Closely allied to 0. bisutui-alis, but is shorter, and spire less 

 acute ; whorls flatter and color darker. 



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



{Chemnitzia.) Proc. Bost. Soc. Nat. Hist., iv. 114. 1851. 

 Shell OA'ate-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. bisidiiraUs, 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. 117. 



(^Chemnitzia.) Proc. Bost. Soc. Nat. Hist.-, iv. 16. 18ol. 



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

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

 cate, sub-rhomboid. 



Length 3.5, diam. 1.5 mill. 



This species is more angular than 0. bis^utKralis, 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. O. BisuTURALis, Say. Fig. 118. 



(Turritella.) Journ. Philad. Acad., ii. 244. 1821. 

 Chemnitzia bisuturalis, Stimpson, Shells of N. England, 43. 1851. 

 Jnminea exif/ua, Couthony, Bost. Jouru. Nat. Hist., ii. 92, t. 2, f. 7. 1838. 

 Odosiomia 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 



