CHIEFLY OF THE UNITED STATES. 275 



Hah. — South America, Don Patricio M. Paz. 



My cabinet and cabinet of Don P. M. Paz and C. M. Wheatley. 

 Diam. 1-1, Length 1-7, Breadth 2-3 inches. 



Shell smooth, nearly round, very much inflated, inequilateral, rounded before and 

 behind; substance of the shell somewhat thick; beaks somewhat prominent and 

 pointed at the tips; ligament very small and dark brown; epidermis dark reddish- 

 brown, rather roughly striate, with distant marks of growth and without rays; umbo- 

 nial slope rounded and leather inflated ; posterior slope elliptical, very slightly carinate, 

 with an obscure slightly impressed line from the beaks to the posterior margin ; 

 anterior cicatrices confluent, rather large and slightly impressed ; posterior cicatrices 

 confluent and very slightly impressed ; dorsal cicatrices imperceptible ; cavity of 

 the shell deep and rounded ; cavity of the beaks shallow and subangular ; nacre very 

 deep red and most beautifully iridescent. 



Soft Parts. — Two males. Branclda rather lai'ge, rounded below, inner one some- 

 what the larger, united the whole length of the abdominal sack. Palpi rather large, 

 round and united only at the upper part. Mantle thin, much thickened at the edges, 

 with numerous small papillse below the branchial opening. Branchial opening rather 

 small, with a few small dark brown papillae on the inner edges. Anal opening dark 

 brown, corrugated on the edges and very long, entirely disunited from the branchial 

 opening below. Has no super-anal opening. Color of the mass dirty-white. 



Remarks. — This very beautiful species has the most intensely red color of the nacre 

 of any species which I have seen. It is almost of a beet-red, and on the broad border 

 this is so intense that in some specimens it is almost black. The border is nearly as 

 large as that oi lato-marginata, and along the line of junction with the pearly nacre 

 the color is deepened. In outline it is between ruhicunda and lato-marginata (nobis), 

 but is not ohovate like the latter, nor so round or carinate as the former, and in color 

 much more deeply colored than any I have seen of either 6f them. In thickness it 

 stands between them. The high wing-like carina of ruhicunda at once distinguishes 

 that species, and the broad thick margin of lato-marginata cannot be confounded with 

 this species. 



Mycetopus PTGM^tJS = Anodonta pijgmoia, Spix. Test. Braz. pi. 23, fig. 3 and 4. 



Soft Parts. — A male. Branchia very wide, slightly curved below, inner ones much 

 the larger, united the whole length of abdominal sack. Paljn large, round Ijelow and 

 united only at the upper part. Mantle very thin, slightly thickened at the edges, 

 having no papilla3 below the branchial opening. Branchial opening rather large, with 

 rather large dark papilla3 on the inner edges. Anal opening corrugated on tlie inner 

 edges, very long, entirely disunited from the branchial opening below. lias no 



