274 MAZATLAtt UNIVALVES 



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

 restore from the overwrought 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 

 separate 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 dentated) mea- 

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

 Mr. Cuming's sp. . '6, *56, '27. 

 Hal). (C. dorsata.) St. Elena; on dead shells, in sandy mud, 

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

 (Var. bilobata.) California ; Mus. Cuming. Mazatlan ; ex- 

 tremely rare, jun., on shells ; L'pool Ccl. 

 Tablet 1354 contains 5 sp. of different ages. In the first, '03 

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

 the deck line has commenced. 



337. CREPIDTJLA EXCAVATA, JBrod. 



C. t. tenuiore, Icevi, oblongd, latere dextro expanso, sinistro 

 convexo ; alba, castaneo varie maculatd, intus nitente ; vertice 

 valde adunco, a margine maxime separato, dextrorsum valde 

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

 apicem depressum monstrante, regulariter crescente ; habitu 

 incrementi subspirali, obliquo, regulari ; septo tenuiori, vix 

 opaco, ad marginem lineas incrementi monstrante. vix in mcdio ; 

 haud aliter sinuato ; oblique et profunde sito, cavitate magnd 

 ad verticetfi ascendente ; limbo acuto. 

 Calyptrsea (Crepidula) e. Brod. in Proc. Zool. Soc. 1834, p. 46 : 



Trans. Zool. Soc. vol. i. p. 205, no. 29, pi. 29, f. 7MtilL Syn. 



Nov. Test. Viv. p. 150. 

 Crepidula e. Desk, in Lam. An, s. Vert. vol. vii. p. 649, no. 19. 



C. _B. Ad, Pan. Shells, p. 226, no. 345. 



