274 MAZATLAN UNIVALVES 
in Mr. Cuming’s Museum, but which he 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 avery 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 Cue (the margin of which is dentated) mea- 
sures F long..°33; ate 31 alt. Wer 
Mr. Cuming’s sp. : SOs. 55o OO 
Hab.—(C. dorsata.) St. Elena; on dead shells, in sandy mud, 
6fm.; Cuming, (teste Brod.:—Valparaiso, teste Mus. Cum.)— 
(Var. bilobata.) California; Mus. Cuming.—Mazatlan ; ex- 
tremely rare, jun., on shells; LZ’ pool Col. 
Tablet 1354 contains 5 sp. of different ages. In the first, °03 
across, the margin is formed, but not the deck: in tle second, 
the deck line has commenced. 
337. CREPIDULA EXCAVATA, Brod. 
C. t. tenuiore, levi, oblonga, latere dextro expanso, sinistro 
convexo ; alba, castaneo varie maculatd, intus nitente ; vertice 
valde adunco, & margine maxime separato, dextrorsum valde 
spiraliter contorto ; nucleo satis magno, discoidali, satis inflato, 
apicem depressum monstrante, regulariter crescente ; habitu 
incrementt subspirali, obliquo, regulart ; septo tenwiore, Vx 
opaco, ad marginem lineas inerementt monstrante, via in medio ; 
haud aliter sinuato; oblique et profunde sito, cavitate magn& 
ad verticem: ascendente ; limbo acuto. 
Calyptreea (Crepidula) e. Brod. in Proc. Zool. Soc. 1834, p. 46 :— 
Trans. Zool. Soc. vol. i. p. 205, no: 29, pl. 29, f. 7.— Mull. Syn. 
Nov. Test. Viv. p. 150. 
Crepidula e. Desh. in Lam. An. s. Vert. vol. vii. p. 649, no. 19.— 
C, B. Ad. Pan. Shells, p. 226, no. 345. 
