89 



A remarkably small and solid species, with a very unusual 

 hinge. It resembles in general small specimens of M. simiUs, 

 but is more triangular and more ventricose, as well as more solid. 

 It is closely allied to 31. cuneola, G. 



LuTEARiA UNDULATA. T. Candida, papyracea, ovata, postice 

 hians, nisi prope marginem posticum concentrice undata, con- 

 cinne rugosa ; apicibus vix anticis ; latere antico rotundato ; 

 latere postico angustato, compresso, ad apicem rotundato ; mar- 

 gine dorsali declivo, rectiusculo, costa submarginali munito. 

 Long. 2J ; alt. 2 ; lat. 1|- poll. Inhabits La Paz, Lower Califor- 

 nia, Lieut. Green. 



Differs from L. canaliculata^ Say, of S. Carolina, in its 

 strictly ovate form, in having the beaks anterior, in having the 

 posterior half less compressed and more gaping, and in the acute 

 ridge bordering the posterior margin. 



LuTRARiA vENTRicosA. T. tcnuis, fragilis, ventricosa, ovato- 

 cuneata, alba, epidermide stramineo rugis remotis radiato in- 

 duta ; apicibus vix anticis, tumidis ; latere antico angustato, com- 

 presso ; latere postico dilatato; facie dorsali valde declivo, an- 

 gulo obtuso limitato, aream latam concavam efformante linea 

 submarginali partitam : intus alba, punctis nitidis notata. Long. 

 3|-; lat. If ; alt. 3 poll. Inhabits Mazatlan, Lieut. Green. 



This would at first sight seem identical with L. carinata, from 

 the coast of Carolina and Florida. But it is more ventricose, 

 less solid, the beak more arching, the region of the posterior 

 margin excavated, and the posterior umbonal ridge obtuse and 

 destitute of a crest. A small African species (Mactra alhida) is 

 a miniature of this shell ; but the posterior slope is less vertical, 

 and there are deeply impressed grooves in front of the beaks. 



Amphidesma flavescens. T. subrotunda, compressa, striis 

 concentricis lamellosis decussatis insculpta, aurantia demum albida 

 et epidermide fusco induta ; apicibus medianis, acutis, baud ele- 

 vatis ; area dorsali antica excavata, postica lanceolata, concava, 

 linea limitala ; intus flavo-tincta punctis nitidis notata ; sinu 

 siphonali spatulato, striis crebris divergentibus insculpta ; fovea 

 ligamentali profunda, elongata ; dente laterali antico ad apicem 



