328 MAZATLAN UNIVALVES 
This species is constituted from a single imperfect specimen. 
in consequence of the peculiar sculpture which has not been 
observed in any other Mazatlan species. The shell appears 
smooth ; but under a high magnifying power, it is found to be 
covered with most minute irregularly concentric wrinkles, like 
the lines on the thumb, or the muscular scar in the operculum 
of Murex nigritus. The plug appears to be mammillated ; but, 
with the aperture, is imperfect. The sculpture, shewing so 
decidedly on a dead shell, must be very beautiful on a perfect 
specimen. Long. °075, lat. ‘017— 022. 
Hab.—Mazatlan ; 1 sp. off Chama; D’pool Col. 
Tablet 1547 contains the specimen. 
376. CECUM DEXTROVERSUM, 7. Ss. 
C. (Fartulum) t. tereti, satis elongata, alba, tenui, levi: septo 
tuimido, submamnutlato, mucrone tumidissimo, dextrorsum later- 
aliter verso ; aperturd parum dechivi, haud contracto ; operculo 
via CONCAVO. 
In this species, as in C. laqueatum, the mucro, instead of 
being in the middle or at the back of the shell, is turned to the 
right ; where in the young shell, which is extremely thin and 
slender, it appears as a conspicuous knob. As the shell 
increases, the body of the plug swells out and becomes mammil- 
lated, so that in certain portions it ean scarcely be told from 
C. glabriforme, especially as the central knob is apt to be 
rubbed off. It is however a larger and more tapering shell. 
The youngest specimen, which only measures ‘023 by *008, 
possesses its operculum. This was also found in three other 
young shells, but all the adult specimens were dead. It ap- 
pears to be nearly flat, but perhaps may become more concave 
in its adult state. The species presents such different appear- 
ances at different periods of its growth, being sometimes long 
and slender, at other times short and stumpy, that it has been 
necessary to preserve a large part of the few found. An un- 
usually large and stout sp. measures Jong. ‘092, Jat. ‘024. 
Hab.— Mazatlan ; very rare, (20sp.) off Spondylus, &e. ; 
*pool Col. 
Tablet 1548 contains 9 specimens, in different stages of 
growth, of which 3 possess their opercula. 
