MAZATLAN BIVALVES 531 
[Famity TELLINID. ] 
686.* Trerrina ————,, sp. ind. (c.) 
Tablet 2521 contains two valves, in form resembling T. dona- 
cilla; 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; L’pool Col. 
[Faminy CARDIADZ. } 
687. CARDIUM ROTUNDATUM, 4%. Ss. 
C. t. parva, equilaterali, ventricosd, albé; costibus circiter 
XX. acutis, vix granosis, quarum ventrales circiter vill. majores ; 
interstitis latis, planatis, vie decussatis ; dent. lat. haud dis- 
tantibus. 
Of this beautiful little shell two opposite valves were found, 
apparently belonging to each other. It resembles C. alabas- 
trum, but with more numerous and less conspicuous ribs. 
Long. °063, lat. * 065. 
Hab.—Mazatlan: extremely rare, off Spondylus ; Z’pool Col. 
Tablet 2522 contains the two valves. 
(Famry KELLIADA,] 
688. LasEA ————, sp. ind. 
Tablet 2523 contains the hinge portion of a shell in shape 
somewhat lke Mactra stultorum ; with most minute and 
erowded concentric striz 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; L’pool Col. 
694. P MonTAcUTA CHALCEDONICA, ”. s. 
?M. t. tenuissimd, interdum opacd, interdum diaphand, cas- 
fanea: ovali, marginibus regulariter excurvatis, umbone pro- 
* No. 685 is Tyleria fragilis, H, ¢ A. Ad. 
