490 MAZATLAN UNIVALVES 



itself being very variable ia shape, sometimes ratber elongated, 

 sometimes squarish. The muscular scar occupies the inner 

 portion, long and narrow. A large specimen measures '22 by 

 '14, and therefore can only make its egress from the adult 

 mouth sideways. This is provided for in the narrow scar, and 

 accounts for the frequent decollation of the apex. — In many 

 hundred specimens however, the nucleus was found to be ab- 

 normal, generally near the middle of the outer margin, as in 

 Bucciniun undatum ; but often nearly central. So common is 

 this state that great confusion might have arisen if the oper- 

 cula had been first described from only a few specimens. 



The smallest adult shell measures '82 by "47 ; the largest 

 specimen long. 1' 3, long. spir.'b'S, lat. '84., div. 80°. 



A slender sp. „ I'l, „ '48, „ '6, „ 60". 



A broad sp. „ -94, „ '35, „ '65, „ 80». 



JIah. — Isle Muerte, Cuming. — Seas of S. America, Deshaycs. — 

 Panama, Col. Jeweit. — Taboga, rare, C. B. Adams. — Mazat- 

 lan, Melchers, Lieut. Green. — Do. ; extremely abundant 

 and fine ; L'pool Col. 



Tablet 2310 contains 7 sp. very young.— 2311, 6 do. a stage 

 older, aperture not contracted. — 2312, 5 do. aperture contract- 

 ing. — 2313, 4 do. labral ridge just appearing. — 2314, 5 do. 

 teeth commencing. — 2315, 5 do. mouth almost complete. 



Tablet 2316 contains 6 sp. adult, broad form.— 2317, 6 do. 

 normal state. — 2318, 6 do. more elevated. — 2319, 6 do. acumi- 

 nate. — 2320, 3 do. with opercula in situ. 



Tablet 2321 contains 3 sp. var. minor, broad. — 2322, 4 do. 

 normal. — 2323, 3 do. acuminate. 



Tablet 2321 contains 3 sp. epidermis removed.— 2325, 3 sp. 

 shoulder pinched.— 2326, 4 sp. incrusted with Bryozoa, &c. — 

 2327, 3 sp. mended after fracture. 



Tablet 2328 contains 12 opercula, normal.— 2329, 6 do. in- 

 crusted with Bryozoa, Annelids, &c. — 2330, 6 sp. nucleus near 

 the center of the outer margin.- 2331, 6 do. nucleus nearer the 

 center of the operculum. — 2332, 6 do. nucleus almost central. — 

 2333, 5 sp. of strange shapes through fracture. — 2334, 3 do. 

 with layers composed of different elements. 



616. COLUMBKLLA STE0MBIF0BMI3, Lam. 



An. s. Vert. ed. Desk. vol. x. p. 266, no. 1. — Sow. Gen. f. 1 : — 

 Thes. Conch, p. 110, no. 1. pi. 36, f. 1, 2.— Val. in Rec. Obt. 



