322 MAZATIAN UNIVALVES 



Sab. — Panama ; common in the sand ; C. B. Adams. — 

 Mazatlan ; 14 sp. off Spondylus &c. ; L'pool Col. 



Tablet 1526 contains 5 specimens in different states. 



369. Cjecum clatheatum, n. s. 



C. (Anellum) t. Jiaud parvd, soUdiore, annulis valde distanti- 

 bus, acutioribus, validis, extantibus, cincta ; interstitiis concavis; 

 septo subplanato, mucronato ; in adultd margine laterali haud 

 monstrante ; mucrone minima, obtusd, pcene in dorsum sitd; 

 operculo ? . . . . 



TMs extremely elegant species is remarkable for its size ; 

 very distant bar-like rings, which are rather sharp ; gracefoUy 

 curved interspaces ; and nearly flat plug with a scarcely pro- 

 minent obtuse mucro, scarcely (if at all) inclined to the right. 

 Only 12 specimens were found. The youngest sp. measures 

 long. '057, lat. -007— "017. The largest, long. '102, lat. (inter- 

 stices) -026, (outside) 'OS. 

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



Tablet 1528 contains 4 specimens of different ages. 



370. CiECUM quadeattjm, n. s. 



C. (Anellum) t. parvd, curtd, solidd, annulis quadratis xii. — 

 XX. cinctd ; interstitiis profundis, guadratis ; aperturd sub- 

 contractd, annulis coneiD'rentibus ; septo mucronato, margine 

 laterali concavo, mucrone parvd, extante, angu^td, subdextrorsum 

 dtd : operculo valde concavo, anfr. circiter x. lined spirali 

 expressd. 



/ Var. coMPACTUM, t. interstitiis parvis seu evanidis, annulis 

 maxime planatis. 



The extreme forms of this shell are singularly different ; at 

 one end of the scale being a larger shell, muricated with 

 squarisl} distant rings, passing into C. clathratum ; at the 

 other, a small stunted state in whifh the rings have so run 

 together that the interstices appear like simple grooves, and 

 the shell approaches the young of C. subimpressum. Among 

 'i3 specimens found, however, (of which 3 possessed opercula,) 

 there appeared too gradual a transition to allow of their separ- 

 ation. At the same time the habit of growth appears quite 

 distinct from that of any of the neighbouring species. It is 

 customary for AucUa to make their rings compact in the mature 



