20 



radiating striae, especially across the disk. Interior tinted (melon) 

 yellow, spangled with shining dots ; siphonal sinus spatulate, veined 

 with numerous diverging striae ; ligament pit deep and long ; ante- 

 rior lateral teeth approximate to beaks. 



Longitudinal, vertical, and transverse diameters two and three 

 eighths, t\vo and one eighth, and one and one fourth inches. 



From San Diego. Lieut. Green. 



Usually found about half this size ; the concentric lamellar strise 

 are then conspicuous ; but these become worn off, and the shell 

 grows more irregular and coarse towards the margin ; the interior 

 is faintly tinted yellow when young, but very richly so when old. 

 It is closely allied to A. corrugatum, Sowb. 



MACTRA NASUTA. 



This species, described in Proceedings Bost. Soc. Nat. Hist., Nov., 

 1851, IV. 88, agrees so nearly with M. falcala, also described 

 by me, (op. cit. III. 216,) that I hesitate to reproduce it as new with- 

 out a direct comparison of the two shells, which I have it not now in 

 my power to make. They will for the present, therefore, be 

 regarded as synonymous. M. falcata^ however, was found at 

 Puget's Sound, while M. nasuta was found by Maj. Rich at San 

 Pedro, and by Lieut. Green, (with a doubt,) at Mazatlan. 



MACTRA MENDICA (PL XV. Fig. 4.) 

 Mactra mendica, Gould; Proc. B. S. N. H., Nov. 1851. IV. 88. 



T. ovato-triangularis, compressa, solida, concentrice striata, epidermide rufa 

 induta ; apicibus antemedianis, acutis, incurvatis, margine dorsali utrinque citb 

 declivi ; latere antico acute rotundato ; latere postico triangular!, desuper viso 

 anguste cordiformi, fortiter striato : intus lactea ; sinu siphonali, parvulo ; fovea 

 Jigamentali retrorsum profunda, dente V-formi parvo ; dentibus lateralibus con- 

 spicuis. 



Shell ovate triangular, small, solid, faintly striated concentrically, 

 and coated with a pale fawn colored epidermis ; beaks antemedian, 

 acute, incurved, dorsal slopes very steep, abrupt, anterior end rather 

 acutely rounded; posterior end triangular, acute angled, with an 

 abrupt ridge along the posterior umbonal ridge, the enclosed poste- 

 rior area is narrow heart-shaped, more coarsely striate, with the 

 lips a little protuberant. Interior milk white ; a very slight siphonal 



