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. CmCUM INSCULPTUM, 2. 8. 
C. (Elephantulum) t.juniore vitred, diaphand, adultd solidé ; 
liris validis quadratis et interstitiis profundis ornatéd ; aper- 
turam versus haud tumente ; septo ungulato, subprominente, 
apice obtuso, paululum dextrorsum verso, margine laterala sub- 
recto; 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. hratocinctum, 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 ssi beds Weert SO20-—Onee 
Hab.—Mazatlan ; extremely rare, off Spondylus, L’pool Col. 
Tablet 1514 contains the perfect specimens, old and young. 
361. CHCUM SUBSPIRALE, 7%. s. 
C. (Elephantulum) t. maxime elongaté, tenuissimé liraté ; 
jucta aperturam annulo subtumente ; septo mucronato, swper- 
ficte subplanato, mucrone laterali, dextrorsum sité, parva, apice 
rotundato, subspirali: operculo coneavo, tenui, anfr. plurimis 
lird tenut spiraliter ascendente. 
Of this beautiful species, a giant among the Ceca, 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 
