MAZATLAN UNIVALVES 325 



5a5.— Mazatlan ; abundant on Spoudylus, not unco mm on on 



Chama, Modiola capax, &c., rare on Ostrea iridescens ; 



L'pool 8f Havre Coll. — PPanama, 1 sp., C. B. Adams. 



Tablet 1531 contains 4 sp. smooth state.— 1532, 11 do. partly 

 smooth, partly waved.— 1533, 4 do. waved state adolescent. — 

 1534, 7 do. adult.— 1535, 2 sp. juu. and 2 adult, with opercula. 



Tablet 1536 contains 4 sp. deformed growth, and 1 pierced by 

 a tiny proboscidean. — 1537, 1 .?p. plug extremely prominent ; 1 

 do. with the profile line very slightly arcuated ; 1 do. deformed. 



Tablet 1538 contams 3 sp. probably belonging to this species, 

 but closely approaching C. la;ve. ' . 



Section C. Fabtulum. 



C. t. IcBvi, cylindraced, scepius utrinque coniracta ; aperturd 

 scepe declivi. 



This group is named from the general resemblance in form 

 to a little sausage. Some species however approach the long 

 tapering Elephantulum, while others are approached by the 

 ringed AneUiim. 



372. C^cum: ljeve, C. B. Ad. (diagn. auct.) 



C. (Fartuhom) t. juniore " C. zwdato" exacte simulante ; 

 t. adultd eidem simili, scd IcBvi, nitidd, haud ujidaid, irJerdv.vi 

 ante apertiiram phis minusve tumidiore ; aperturd et apice 

 minus contractu ; operculo concavo, suturis minus distinctis, 

 texturd semicornea, hrunneo tincfd. 

 C. B. Ad. Pan. Shells, pp. 162, 311, no. 214. 



Tliis shell, imperfectly described by Prof. Adams from two 

 specimens varying in age, is so remarkably like C. undatum 

 not only in its general habit but in several minute particulars, 

 and especially in the shape of the plug and mouth, that aber- 

 rant individuals of each are very difficult to distinguish. I 

 know of no character by which the young shells can be separ- 

 ated. Wlven it arrives at the "monstrosum" stage, the 

 absence of undulated rings in the bowl of the pipe becomes a 

 marked and uniform character. In the adult, the cylinder is 

 rather less contracted at the two ends, and the aperture a 

 trifle less slanting. Before the contraction of the aperture, 

 the tube is sometimes swollen, which has never been observed 



Sept. 1856. ee 



