MAZATLAN UNIVALVES 295 
This group, first distinguished by Schum., 1s characterized 
by its free, semi-tubular lamina, like a cornucopia divided 
longitudinally. It may be regarded as a Crepidula with each 
marginal sinus intensified ; or as a Crucibulum with the lamina 
free instead of being turned round upon itself. A full descrip- 
tion of the animal of one species is given by Owen, loc. cit. It 
is probable that the young will be found to commence like 
Crepidula. The genus is represented in the Mazatlan collec- 
tion by asingle specimen. In all the species examined, the 
plane of increase is more or less perpendicular to the base, as 
in Capulus. The habit of growth is generally extremely 
irregular, as in Hipponyx, which at least some of the species 
~ resemble in possessing a shelly plate of adherence. As far as 
can be judged by the specimens in the Cumingian Museum, 
the species which Brod. has constituted in this group are all 
well founded. C.corrugata has an exterior like Crucibulum 
umbrella, Desh. (=rudis, Brod.) The other three species differ 
in the growth of the cup: that in C. cepacea is produced 
forward, and oceupies not much more than a semicirele ; in 
C. varia, it grows straight up, occupying three-fourths of a 
circle; in C. cornea, it is compressed, lengthened, with pro- 
jecting points, and the opening very small. 
345. CALYETREA CEPACEA, Brod. 
Proc. Zool. Soc. 1834, p. 35:—Trans. Zool. Soc. vol. i. p. 197, 
pl. 27, f. 4.—Miill. Syn. Nov. Test. Viv. p. 142.—Lam. An. s. 
Vert. vol. vii. p. 633, no. 24.— Rev. Zool. Cuv. Soe. July, 
1838.—Chénu, Lec. Hlem. p. 144, f. P462.— Mike. Zeit. f. Mal. 
1851, p. 36, no. 128.—C. B. Ad. Pan. Shells, p. 220, no. 332. 
This shell is easily distinguished from the W. Indian species, 
C. equestris, &c. both by the vertex and the markings. The 
nucleus consists of an elevated spiral body, like Bithinia. (The 
apex is unfortunately wanting.) ‘The spire axis is fixed horizon- 
tally. The sculpture of the shell consists of extremely fine, 
close, radiating lines, which under the microscope are found 
to be sharp ridges, with semicircular spaces between, crowded 
with concentric (semicircular) striae. Long. 54, lat. °65, alt. *23. 
Hab.—Isl. Muerte; on dead shells, in sandy mud, 11 fm. ; 
Cuming.—Panama ; extremely rare, on dead shells, at low 
water mark; C. B. Adams.—Mazatlan, Menke:—one sp, 
Ppool Col. 
Tablet 1461 contains the specimen. 
