215 



bonibus latis, elevatis, fere medianis : cardo dente parvo, conico 

 instructa : sinu palleali lato, arcuato, minime impresso; cicatrice 

 musculari postica discreta, crescentiformi. Long. 2J ; alt. 2 ; 

 lat. 1^. Hah. Rio Negro, Patagonia. 



Besides being destitute of ribs, it is more nearly equilateral 

 than P. arctica, and has the beaks more posterior. It is less 

 gaping, and the posterior truncation is scarcely oblique. 



PANOPiEA GENEROSA. Tcsta magna, ponderosa, calcarea, 

 sub-quadrilateralis, concentrice unduloso-plicosa, epidermide fla- 

 vido, rugoso induta, anlice rotundata, postice truncata et valde 

 hians ; umbonibus submedianis, aculis, elevatis, undulatis : cardo 

 gracilis, dente elevato oblique triangular! instructus : cavitas ad 

 apicem profunda ; cicatrice musculari lato, bene impresso ; sinu 

 siphonali minime profundo. Long. 6 ; alt. 4 ; lat. 3 poll. Hab. 

 Puget Sound, Oregon. 



This large species stands by the side of P. Aldrovandi, but is 

 distinguished by the form of the anterior extremity. 



Mya pr^cisa. T. M. truncatm similis, calcarea, epider- 

 mide corneo induta, ovata, antice rotundata et ventrlcosa, postice 

 angustata, compressa et truncata ; cardo dente trapezoideo, 

 latiore quam elevato, postice declivo instructa; linea palleali 

 angusta, crenata ; sinu siphonali profundo, arcuato; cicatrice 

 anteriori elongato, falciformi. Long. 2^ ; lat. 1 ; alt. 1 J poll. 

 Hah. Puget Sound. 



Differs from M. truncata in being more narrowed posteriorly, 

 more rounded anteriorly, more inflated at the umbonal slope, in 

 its narrow palleal impression and deeper siphonal sinus, and 

 more particularly in having the tooth slope backwards. 



Mactra deluta. T. tumida, ovato-rotundata, hiantissima 

 sordida, epidermide tenui deluto, oblique corrugato induta, con 

 centrice undulata ; umbonibus submedianis, tumidis, incumben 

 tibus, contiguis; margine dorsali utroque declivi ; margine ven 

 trali rotundato; lateribus obtusis : cardinis fovea ligamentali 

 profunda; dente V-formi gracili, ramis inequalibus ; dentibus 

 lateralibus brevibus, trigonis, compressis ; sinu siphonali prope 

 centrum valvse obducto. Long. If; alt. If; lat. ly^ poU* Hah. 

 New Zealand. 



The external appearance is rather that of a rude Venus, and 



