274 MAZATLAN tTNlVALVIS 



in Mr, Cuming's Museum, but wbicb. lie has allowed me to 

 restore from the over-wrouglit figures in the Transactions. It 

 is closely related to some forms of C. dilatata, jun. 



The mode of growth in the young shell is as in C. nivea, &c. 

 The vertex is rather large, "02 in. or upwards across, Velutina- 

 shaped, smooth, with a rather sunken apex and rapidly increas- 

 ing whirls. On commencing the permanent form, it spreads a 

 film over the base of the spire and a very large margin all 

 round. The deck commences at a considerable angle from this 

 film, first as a marginal line, then gradually developing till the 

 lobes are formed. The vertex is rather prominent, but not 

 eeparate from the body of the shell. Some of the shells are 

 more solid than Mr. Cuming's adult specimens ; and further 

 agree with the typical C. dorsata in being of a yellowish cast, 

 with the deck rather brown. The subdiaphanous white 

 specimens are sometimes spotted with chesnut. The largest 

 Mazatlan specimen, (the margin of which is deutated) mea- 

 sures . . long. '33, lat. '37, alt. '12. 

 Mr. Cuming's sp. . » '6, „ '56, ,, "27. 

 Sah.—iC. dorsata.) St. Elena; on dead shells, in sandy mud. 

 6 fm. ; Cuming, (teste Brod. :— Valparaiso, teste Mus. Cum.)— 

 (Var. bilobata.) California ; Mus. Cimiing.— Mazatlan ; ex- 

 tremely rare, jun., on shells ; L'jpool Col. 

 Tablet 1354 contains 5 sp. of difi'erent ages. In the first, "03 

 across, the margin is formed, but not the deck : in the second, 

 the deck line has commenced. 



337. Ceepidula excavata, Brod. 



C. t. tenuiore, lavi, oblongd, latere dextro expanso, sinistra 

 convexo ; albd, castaneo varie maculatd, intus niteiite ; vertice 

 valde aduiico, a margine maxime separata, dextrorsum valde 

 spiraliter contorto ; nucleo satis magno, discoidali, satis injlato, 

 apicem depressum mon-strante, regular iter crescente ; habitu 

 incrementi suhspirali, obliquo, regiilari ; septa tenuiori, vix 

 opaco, ad marginem lineas incrementi monstrante, vix in medio ; 

 haud aliter sinuato ; obliqtie et profimde sito, cavitate magnd 

 ad verticeth asccndcnte ; limbo acuta. 

 Calyptraa (Crepidula) e. Brod. in Proc. Zool. Sac. 1834, p. 46 :— 



Trans. Zool. Soc. vol. i. p. 205, no. 29, pi. 29, f. I.—Miill. Syn. 



Nor. Test. Viv. p. 150. 

 Crepidula o.DesJi. in Lam. An. s. Vert. vol. vii. p. 649, no. 19.— 



C. B. Ad. Fan. Shells, p. 226, no. 346. 



