MAZATLAN UNIVALVES 281 
=Crepidula unguiculug, var. Brod. in Mus. Cum.—|[Tanacus 
unguiculus, Sow. Publ) H. & A. Ad. Gen. 1. 370. 
°?=Crepidula Patagonica+C. protea, D’ Orb. (pars,) B. M. Cat 
Moll. p. 48, no. 416, 417. 
Comp. Crepidula Navicelloides, Nutt. in Jay’s Cat. p. 107, 
no. 3035, (Upper California.) 
Comp. Crepidula explanata, Gould, Cal. & Mex. Shells, p. 4, 
pl. 14, f. 7.=Calyptrea perforans, Var Voy. Ven. 1846, pl. 24, 
f.9, 9a, 6. [The author seems to imply that the creature 
burrows : the specimen represented however has evidently 
been developed in the hole of a Lithophagus. |=C. exuviata, 
Nutt. in Jay’s Cat. p. 107, no. 3027. ' 
This creature, when flat and finely grown, is,the C. squama 
of Brod. The same shell, when coarsely grown, more convex 
and without brown stripes, is the C. nivea of C. B. Ad. When 
the layers of which C. nivea is composed, instead of lying 
regularly one over the other, are slightly prominent, it becomes 
the C. striolata, ke. When they are drawn forwards and 
project, it becomes the C. Lessonii, Brod. The name of Prof. 
Adams is retained, in preference to the prior ones of Broderip 
and Menke, as representing the normal condition of the shell. 
The name C. unguiculus has priority, but does not appear to 
have been published. Among the specimens marked C. protea 
and C. Patagonica by D’Orb. in his collections, there are 
several w hich ; seem to belong to this species ; others to C. onyx, 
&e. v. supra. Both are mernred by Dr. Gray to C. dilatata, 
(B. M. Cat. D’ Orb. Moil. p. 49.) 
C. nivea begins life as a minute Velutina-shaped body, with 
a sunken apex and coarse concentric folds. When this has 
grown to about °015 across, it suddenly enlarges itself, throws 
a columellar lip over the base of the shell, raises a more or less 
prominent margin round it, so as to surround the vertex, and 
commences its septum at an angle from the columellar lip 
varying from about 90° at the posterior to 130° at the anterior 
end. The smallest shell found measures *045 in length, on 
which these stages are distinctly traceable. The septum is at 
first straight, then angulated in the middle, lastly with an 
anterior sinus. 
In the ‘squama’ stage, it appears as a very thin flat shell; 
with the vertex generally lustrous brown, sometimes white ; 
from this radiate a greater or less number of brown lines, 
sometimes more or less broken into dots, gradually losing 
