460 MAZATLAN UNIVALVES 



* 



Mitra lens, Rve. Conch. Ic. pi. 1, f. 1. — Mhe. in Zeit. f. Mai. 



1851, p. 35, no. 120.— C. B. Ad. Pan. Shells, p. 42, no. 17.— 



H. ^' A. Ad. Gen. i. 169. 

 Tiara foraminata, Sioains. ms. ; JBrod. Froc. Zool. Soc. 1835, 



p. 194. 

 Mitra Dupontii, ^ien. Icon. Conch, p. 43, pi. 13, f. 39. 



This species varies very mucli in growth and sculpture ; but 

 is almost al,wajs recognized b,y the deep punctures which occur 

 at irregular distances in the middle of the whirl, causing tuber- 

 cles to rise up within. Between these are numerous broad 

 costce, 8 — 13 in a whirl, more or less obsolete in the adult. 

 These are crossed in the young shell, by numerous fine, more 

 or less sharp spiral ridges ; which at varying periods of growth 

 become rounded and finally obsolete. At the same time 

 impressed spiral lines often appear, connecting the pits. When 

 adult, the columella has 3 plaits, with a fourth underneath, 

 rudimentary. In the yoimg shell this is absent ; and the third 

 is often rudimentary, rarely absent. The shell is covered with 

 a smooth, close, dark olive or brownish epidermis ; and is 

 generally densely incrusted with coralline. Underneath it is 

 of an ashy brown, sometuues light, sometimes very dark. The 

 largest sp. measures long. 2 '4, loiig. spir. 1'34, lat. "94, div. 30". 

 A broad sp. „ ,, 1"35, „ "65, ,, '6, „ 50". 



A narrow sp.„ ,, 1'48, „ '8, „ "54, „ 30". 



Sah. —Vanama., St. Elena, and Is. Plata ; in sandy mud, 

 6 — 14 fm.; Cum'mcf. — Panama, very rare, C. B. Adams.— 

 La Paz, Major Rich. — Mazatlan ; not uncommon ; L'x)ooV^Sf 

 Havre Coll. 



Tablet 2091 contains 4 sp. elongated form.— 2092, 5 sp. nor- 

 mal state.— 2093, 4 sp. broad.— 2094, 7 sp. shewing changes of 

 sculpture. — 2095, 2 sp. after acid process, shewing colour. — 

 2096, 1 sp. curiously eroded.— 2097, 1 sp. with egg-cases. 



Tablet 2098 contains a young specimen, strongly and 

 closely sculptured, but without pits. Deeply cut lines however 

 appeal', in which the pits would probably have afterwards 

 appeared. 



Tablet 2099 contains a small acuminated sp. without pits, 

 costa; narrow and distant, spiral sculpture nearly obsolete, 

 columella biplicate. Were it not for the great variation in the 

 ordinary specimens, this would have been regarded as a dis- 

 tinct species. 



