MAZATLAN UNIVALVES 295 



This group, first distinguished by Sc/tum., is 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 a single 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, Desk. (=rudis, Brod.} The other three species differ 

 in. the growth of the cup: that in C. cepacea is produced 

 forward, and occupies not much more than a semicircle ; 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. CALYPTR^A CEPACEA, Brod. 



Proc. Zool. Soc. 1834, p. 35 -.Trans. Zool. Soc. vol. i. p. 197, 

 pi. 27, f. <LMiiU. Syn. Nov. Test. Viv. p. 142. Lam. An. s. 

 Vert. vol. vii. p. 633, no. 24. Rev. Zool. Cuv. Soc. July, 

 1838 Chenu, Lee. Elem. p. 144, f. P462. Wee. Zeit.f. Mai. 

 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. 

 Hob. 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. 

 L'pool Col. 

 Tablet 1461 contains the specimen 



