87 



concavo ; umbonibus antemedianis, acutis, parum elevatis ; epi- 

 dermide olivaceo-glaucescente fluctuatim corrugato induta : ca- 

 vositas argentea ; disco salmonaceo : cardo edentulus vel potius 

 papilla cardinali in valva dextra instructus. Long. 1|; alt. |- ; 

 lat. £ poll. Hab. Peru. 



The peculiar dead rusty-green color of the epidermis, with its 

 loop-like corrugations may serve as distinctive marks. It would 

 come under the genus Monocondylea of D'Orbigny. 



Anodon feminalis. T. solidula, transversa, ovato-triangif- 

 laris, antice acuminata, margine postico in margine dorsali con- 

 tinuo, arcuato; margine ventrali recto; apice rectangulari ; 

 umbonibus inconspicuis, erosis, anticis, declivitate posticali 

 obtuse angulato ; epidermide lamelloso, piceo : margarita pur- 

 purascens ; limbo argenteo ; dente cardinali obsoleto. Long. 

 2£; alt. 1£; lat. £ poll. Hab. Oregon. 



At first this was supposed to be the young of A. angulata, 

 Lea ; but it proves different in several constant characters, be- 

 sides its widely remote habitat. It is much smaller and thinner, 

 its surface rude and dusky, instead of smooth and green ; its 

 outlines are all curves instead of right lines ; the dorsal and ter- 

 minal outlines form a continuous curve instead of a distinct 

 angle ; the beaks are more anterior and the cardinal apophysis 

 is never found in A. angulata, while it is constant in this. 



Anodon cognata. T. fragilis, transversa, oblongo-ovata ; 

 margine dorsali brevi, recto ; margine ventrali arcuato ; latere 

 antico rotundato ; latere postico oblique truncato, ad apicem rotun- 

 dato ; disco turgido ; epidermide virescente, nitido; umbonibus 

 antemedianis inconspicuis, undulatis : margarita livido-albida. 

 Long. 3 ; alt. 1^ ; lat. 1 poll. Hab, Nisqually and near Fort 

 Vancouver. 



Resembles small specimens of A. cygnea ; but the dorsal 

 margin is shorter, not continuously straight, and forming an 

 abrupt angle above, anteriorly ; the posterior extremity is less 

 acute and more nasute ; the cavity of the beaks is also somewhat 

 over-arched. Excepting the beaks, it is like A. Jluviatilis. 



Alasmodon falcata. T. transversa, valde inequilateralis, fal- 

 cata, antice rotundata, postice deflecta, acuta, marginibus subpa- 

 rallelis ; disco sub-excavato ; umbonibus obtusis, erosis ; epider- 



