MAZATLAN UNIVALVES 281 



= Crepidula unguiculus, var. Brod. in Mus. Cum. [lanacus 

 unguiculus, Sow. ?ubi) H. fy A. Ad. Gen. i. 370. 



? = Crepidula Patagonica + C. protoa, 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, 

 pi. 14, f. 7. = Calyptra?a perforans, Vol. Voy. Yen. 1846, pi. 24, 

 f. 9, 9 a, b. [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 Jays 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 Ia3 r ers of which C. nivea is composed, instead of lying 

 regularly one over the other, are slightly prominent, it becomes 

 the C. striolata, Mke. 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 which seem to belong to this species ; others to C. onyx, 

 &c. v. supra. Both are referred by Dr. Gray to C. dilatata, 

 (B. M. Cat. D'Orb. Moll. 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 line^, 

 sometimes more or less broken into dots, gradually losing 



