390 MOLLUSCA. 
Figures 535, 535 a, lateral and dorsal views of the shell ; 535 8, inte- 
rior, with the hinge. 
Mactra cunEota (Gould. ) 
T. parva, crassiuscula, rudis, ovato-cuneata, allida, epidermide stra- 
mineo induta, concentricé striata; umbonibus submedianis, tumidis, 
acutis, anteversis ; latere antico angustato, subacuto ; latere siphonah 
breviort, tumidiori, subtruncato: area cardinalis minima ; fovea liga- 
mentali indistincta ; dente V-formi conspicuo; dentibus lateralibus 
curtis, elevatis ; sinu siphonali minimo, quadrantem teste solum trans- 
seunte. 
Mactra cuneola, Goutp; Proceed. Boston Soc. Nat. Hist., i. 216. 
May 1850. Expedition Shells, 75. 
SHELL very small, thin, transversely ovate, wedge-shaped, nearly 
equilateral, white, with a thin, closely adhering straw-coloured epider- 
mis; surface smooth and shining, with pretty regular and conspicuous 
concentric strie# ; anterior end much the narrowest, subtriangular, sub- 
acute at tip; posterior end more tumid, with a decided angular, um- 
bonal slope ; outline somewhat rectilinear ; tip broad, subtruncate ; ven- 
tral edge rectilinear at the middle; anterior dorsal edge cuneate, with 
a large ill-defined area; posterior dorsal edge broad-ovate, moderately 
convex ; beaks delicate, papillary, not touching. Valves convex, espe- 
cially posteriorly ; hinge area very delicate; lgamentary pit inconspi- 
cuous; V-tooth well-developed, prominent; lateral teeth elevated, 
short, triangular; siphonal sinus very small, extending scarcely one- 
fourth across the shell. 
Length five-eighths of an inch; height half an inch; breadth three- 
tenths of an inch. 
Inhabits Callao, Peru. 
In most of its characters this little shell corresponds with our M. 
lateralis, only that in this shell it is the posterior end which is shortest 
and broadest, whereas the reverse is the case in that shell. 
Figures 504, 504 a, lateral and dorsal views of the shell; 5044, 
interior, with the hinge. 
