MAZATLAN UNIVALVES 355 



Two specimens of this species were found, differing some- 

 what in the prominence of the angular keels. It displays no 

 trace of callosity on the pillar lip, and is known at once from 

 Isapis maculosa by the acute spire, and the very fine spiral 

 stria) and keels. The older (worn) specimen measures long. '07, 

 long. spir. '025, lat. "063, div. 80. 

 Sab. Mazatlan ; 2 sp. off Spondylus ; L'pool Col. 



Tablet 1701 contains the fresh specimen, almost translucent. 



SUBGENUS ISAPIS, H. $ A. Ad. 



Gen. vol. i. p. 320. Part of the diagnosis of this group is 

 only of specific value, being founded on the ? Narica anomala, 

 C. B. Ad. (Contr. Conch, no. 7, p. 109,) from Jamaica. The 

 Mazatlan species agree exactly with Fossarus except in the 

 columellar plait, which is. obtuse and small in I. ovoidea, 

 (Narica ovoidea, Gould, Cal. fy Mex. Shells, p. 7, pi. 14, f. 10, 

 "purchased at Mazatlan, Col. Jewett ;") and in I. maculosa 

 is almost obsolete. A similar structure appears in Purpura 

 columellaris : in Cuma tectum, it becomes a Turbinelloid fold. 



406. ISAPIS MACULOSA, n. s. 



I. t. subovoided, inflatd, tenui ; albidd, f us co-pur pur eo macu- 

 losa, subnacred ; apice planato ; anfr. iii., rapide augentibus ; 

 liris spiralibus validis, extantibus, subquadratis, circiter x., 

 quarum iv. in anfr. penult, videntur, duceque umbilicum magnum 

 entrant; interstiiiis tenue cancellatis ; epidermide sublamel- 

 losd ; peritremati continuo ; labro acuto, a liris palmulato, 

 intus sculpturam externam monstrante : labio vix arcuato, 

 callositate mediand, obtusd, inconspicud munito. 



Differs from I. ovoidea in its small size, depressed spire, 

 flattened vertex, shouldered whirls, deeply spotted surface (the 

 spots being conspicuous even in a very dead shell), scarcely ex- 

 cavated labium, and very obtuse deposit, which can hardly be 

 seen except in the broken shell. In other respects there is a 

 great correspondence. The lustrous hue of the interior is a 

 good distinguishing character. Long. '118, long. spir. '038, 

 lat. '112, div. 90. 

 Hab. Mazatlan ; extremely rare ; L'pool Col. 



Tablet 1702 contains a beautiful young specimen, '035 by 

 '025, and a perfect adult. 



