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 
strie and keels. The older (worn) specimen measures long. *07, 
long. spir. °025, lat. °063, div. 80°. 
Hab.—Mazatlan ; 2 sp. off Spondylus ; L’pool Col. 
Tablet 1701 contains the fresh specimen, almost translucent. 
SuscEenus 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. § Mex. Shells, p.7, pl.14, £. 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, %. s. 
T. t. subovoided, inflata, tenui ; albidd, fusco-purpureo macu- 
lost, subnacred ; apice planato; anfr. i1., rapide augentibus ; 
liris spiralibus validis, extantibus, subquadratis, circiter X., 
quarum v.in anfr. penult. videntur, dueque umbilicum magnune 
entrant ; interstitiis tenue cancellatis ; epidermide sublamel- 
lost; peritremati continuo; labro acuto, a liris palmulato, 
intus sculpturam externam monstrante : labio vix arcuato, 
callositate mediand, obtusd, inconspicud muntto. 
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. ong. ‘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. 
