MAZATLAN UNIVALVES 325 
ITab.—Mazatlan ; abundant on Spondylus, not uncommon on 
Chama, Modiola capax, &c., rare on Ostrea iridescens ; 
L’pool & Havre Coll.—? Panama, 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. jun. and 2 adult, with opercula. 
Tablet 1536 contains 4 sp. deformed growth, and 1 pierced by 
a tiny proboscidean.—1537, 1 sp. plug extremely prominent; 1 
do. with the profile line very slightly arcuated ; 1 do. deformed. 
‘Tablet 1538 contains 3 sp. probably belonging to this species, 
but closely approaching C. lve. 
Section C. Fartrunum. 
C. t. levi, cylindraced, sepius utrinque contractéd ; apertura 
sepe 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 Anellum. 
372. Cacum Leven, C. 3B. Ad. (diagn. auct.) 
C. (Lartulum) t. ee re “CO. undaio” exacté simulante ; 
t. adultd eidem simili, sed levi, nitidd, han. undatd, Bs 
ante aperturam plus minusve tumidiore; apertura et apice 
minus contractad ;° operculo concavo, suturis minus distinctis, 
teaturd semicorned, brunneo tincté. 
C. B. Ad. Pan. Shells, pp. 162, 311, no. 214. 
This shell, imperfectly described by Prof. Adams feom two 
specimens varying in_age, is so remarkably like C. undatum 
not only in its general habit but in séveral 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. When 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. . €e 
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