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 long. '15, lat. '16, alt. '09. 

 Sab. Mazatlan ; in shell washings, between the ribs of Cardia, 



in crevices of Chamae and Spondyli, &c., not uncommon ; 



If 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. LUCINA PBOLONGATA, n. ,?. 



L. t. parvd, Jlavidd, solida ; antice, maxime prolonga- 

 t a : marginibus rotundatis, lunulci longd, umbonibus antice 

 incurvatis ; liras concentricas rotundatas plus minusve mon- 

 strante ; intus dent, crassioribus, lat. subapproximatis ; impres- 

 sionibus muscularibus regularibus, subovalibus ; margine interno 

 seu planato sew cremdato : ligament parvo, externo. 



Shell somewhat resembling L. calculus, Rve. (Conch. Ic. pi. 11, 

 f. 68, taken in coarse sand, 10-13 fm., G-ulf of Nicoyia, CumingJ 

 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. 

 Hob. Mazatlan ; from the crevices of Chamse and Spondyli, 



very rare ; L'pool Col. 



Tablet 474 contains a large and a small pair, and 5 valves 

 differing in age and markings. One, having been bored by a 



