MAZATLAN UNIVALVES 315 



inconstant character, as in Siphonaria. The habit of growth 

 also is very similar in all. Prof. Adams only found two specimens 

 belonging to this group, which he called C. laqueatum ; the 

 fortunate circumstance of one being in the Cumingian collec- 

 tion enables us to complete the imperfect description in Pan. 

 Shells, no. 215, pp. 162, 311. The plug is found to be of unique 

 formation, being mammillate over the principal surface, with a 

 separate rather prominent lateral tubercle, which is somewhat 

 s nistral. 



360. CAECUM INSCULPTUM, n. s. 



C. (Elephantulum) t.juniore vitred, diaphana, adult a solidd ; 

 liris validis quadratic ct interstitiis profundis ornatd ; aper- 

 turam versus haud tumente ; septo ungulate, subprominente, 

 apice obtuso, paululum dextrorsum verso, margine later all sub- 

 reclo ; operculo ? . . . . 



Only one young and one adult specimen, besides fragments, 

 were found of this species. The young shell is as transparent 

 as glass, and of exquisite beauty. The adult is solid, bearing 

 deeply cut sculpture. It is known from C. liratocinctum, by 

 the absence of rings, the squareness of the ribs and depth of 

 the interstices ; and by the plug which is somewhat interme- 

 diate between the ungulate and mucronate forms, rising in a 

 nearly straight and regular line to an obtuse apex which is 

 turned somewhat to the side in both specimens. The young- 

 est measures long. "053, lat. '013, "017* 



The largest "133, '023 '028. 



Hab. Mazatlan ; extremely rare, off Spondylus, L'pool Col. 



Tablet 1514 contains the perfect specimens, old and young. 



361. CJECUM STJBSPIEALE, n. s. 



C. (Elephantulum) t. maxime elongatd, tenuissime liratd ; 

 juxta aperturam annulo subtumente ; septo mucronato, super- 

 fide subplanato, mucrone laterali, dextrorsum sitd, parvd, apice 

 rotundato, subspirali : operculo concavo, tenui, anfr. plurimis 

 lira tenui spiraliter ascendente. 



Of this beautiful species, a giant among the Caeca, being no 

 less than a tenth and a half of an inch in length, 6 perfect and 

 6 broken sp. were found. It is known by the finely striated and 



