100 MAZATLAN BIVALVES 
Though 200 valves were found, many of them fresh from the 
banquets of carnivorous Gasteropoda, there was only one pair. 
When young, nothing is seen but the concentric ridges; the 
shell is then elongated anteriorly, and scarcely to be distin- 
guished from the young of L. prolongata; afterwards it assumes 
a regular, rounded form, with the posterior part flattened, and 
bearing fewer but more elevated ribs. The radiating ribs first 
appear at different ages, and are very close and little raised. 
The margin is often not crenated in the young shell. The 
smallest valve is only ‘03 across; an unusually large one 
measures Jong. ‘15, lat. °16, alt. O09. 
Hab.—Mazatlan ; in shell washings, between the ribs of Cardia, 
in crevices of Chame and Spondyli, &c., not uncommon ; 
T’pool Col. 
Tablet 472 contains the pair, and 14 valves of different ages. 
Tablet 473 contains 3 valves, which may be an elongated 
variety of this species, or the young of L. prolongata. 
145. LuciINaA PROLONGATA, %. Ss. 
Lt. parva, flavida, solida ; antice, maxime prolonga- 
; Ae : % 5 ? : 
ta: marginibus rotundatis, lunula longa, umbonibus antice 
incurvatis ; liras concentricas rotundatas plus minusve mon- 
strante ; intus dent. crassioribus, lat. subapproximatis ; impres- 
sionibus muscularibus regularibus, subovalibus ; margine interne 
seu planato seu crenulato : ligamento parvo, externo. 
Shell somewhat resembling L. calculus, Rve. (Conch. Ic. pl. 11, 
f. 68, taken in coarse sand, 10-13 fm., Gulf of Nicoyia, Cuming,) 
which however is described as smooth, polished, shining white. 
This is of a yellowish cast; and though the rounded ridges are 
often nearly obsolete, yet it is never polished. On one speci- 
men were 3 deeply cut concentric sulci. The young shell has 
its ribs sharper, when it resembles L. Mazatlanica. The pos- 
terior part is rounded off. Inside there is a glossy deposit over 
the mantle part, the margin being very finely rugose. The 
muscular scars in this species and the last are much more 
equal than in the typical forms. The smallest valve is “04 
across; the largest measures long. ‘16, lat. °13, alt. °08. 
Hab.—Mazatlan ; from the crevices of Chamez and Spondyli, 
very rare; L ool Col. 
Tablet 474 contains a large and a small pair, and 5 valves 
differing in age and markings. One, having been bored by a 
