328 MAZATLAfr 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 maiumillated ; 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. 



ITab. Mazatlan ; 1 sp. off Chama ; L'pool Col. 

 Tablet 1547 contains the specimen. 



376. C^CUM DEXTBOVEBSUM, n. s.- 



C^(Fartulum) t. tereti, satis elongata, alba, tenui, lavi : septo 

 tumido, submammillato, mucrone tumidissimo, dextrorsum later- 

 aliter verso ; apertura parum declivi, haud contracto ; operculo 

 vix 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 can 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 long. '092, lat. '024. 



Hob. Mazatlan ; very rare, (20 sp.) off Spondylus, &c. ; 

 L'pool Col. 



Tablet 1548 contains 9 specimens, in different stages of 

 growth, of which 3 possess their opercula. 



