MAZATLAN BIVALVES 531 



[FAMILY TELLINID^S.] 

 686.* TELLINA , sp. ind. (c.) 



Tablet 2521 contains two valves, in form resembling T. dona- 

 cilia; but with, external concentric sculpture continuous instead 

 of alternating. The young shell is extremely thin, with the 

 sculpture in sharp ridges, rosy ; the larger is very thick for its 

 size, yellowish, with the ridges broad and rounded. It is proba- 

 ble that they belong to different species. Inside with a strong 

 bifid tooth between two pits ; lateral teeth none. 

 Hab. Mazatlan; extremely rare, off Spondylus; IS pool Col. 



[FAMILY CAEDIAD^E.] 



687. CAKDIUM BOTUNDATUM, n. s. 



C. t. parvd, ceguilaterali, ventricosd, alba ; costibus circiter 

 xxii. acutis, vice granosis, quorum ventrales circiter viii. majores ; 

 interstitiis latis, planatis, vix decussatis ; dent. lat. Jiaud dis- 

 tantibus. 



Of this beautiful little shell two opposite valves were found, 

 apparently belonging to each other. It resembles 0. alabas- 

 trum, but with more numerous and less conspicuous ribs. 

 Long. "063, lat. '065. 

 Sab. Mazatlan : extremely rare, off Spondylus ; If pool Col. 



Tablet 2522 contains the two valves. 



[FAMILY KELLIAD^S.] 



688. LASEA , sp. ind. 



Tablet 2523 contains the hinge portion of a shell in shape 

 somewhat like Mactra stultorum ; with most minute and 

 crowded concentric strise on the epidermis ; inside with two 

 slender lateral teeth, and a hinge pit near the umbo under one 

 of them. 

 Hab. Mazatlan ; 1 sp. in Spondylus ; IS pool Col. 



694 P MONTACUTA CHALCEDONICA, n. S. 



?M. t. tenuissimd, interdum opacd, interdum diapJiand, cas- 

 taned : ovali, marginibus regulariter excurvatis, umbone pro- 



* No. 685 is Tyleria fragilis, S. $ A. Ad. 



