134 THE NAUTILUS. 



A NEW ANODONTA. 



BY CHAS. T. SIMPSON. 



Anodonta mearnsiana. 



Shell rhomboid, compressed anteriorly, inflated posteriorly, gener- 

 ally smooth and shining, covered with rather sulcate growth lines, 

 moderately solid in structure, having a thin epidermis, which is 

 easily worn off, and varying from yellowish to olive-green in color ; 

 beaks sculptured with some half dozen undulations, which are acute 

 posteriorly, and rounded anteriorly. The female shell exhibits a 

 considerable degree of inflation extending from some distance back 

 of the beaks to the posterior- ventral region, and with the male shell 

 occasionally shows a couple of slight sulcations running from the 

 umbones along the dorsal slope. 



The upper part of the anterior curve is rather more prominent 

 than the lower ; the ventral region is sometimes slightly emarginate 

 in the center of the females ; and there are occasional slight traces 

 of biangulation posteriorly in the shells of both sexes. Nacre a soft 

 silvery color, inclining to a lurid brownish in the quite shallow cavity 

 of the beaks; and near the rather straight hinge line; the brown 

 patch or scar at the end of the nearly concealed ligament rather 

 elongated ; cicatrices rather distinct. 



Mantle large, thin, not heavily bordered, brownish in the region 

 of the fringes and anal opening, whitish elsewhere; fringes few, 

 fleshy, and rather pointed. Branchiae moderate, the inner slightly 

 larger, and darker than the outer; branchial opening large, 

 furnished with a few rather short, fleshy papillse. Palpi elongated, 

 pointed at the posterior, united for three-fourths of their length. 

 Foot solid, rugose. Anal opening large, not furnished with papillse ; 

 super-anal opening small, removed to some distance above the anal 

 opening. 



Length from anterior to posterior ends 85, breadth 45 mm. ; 

 diameter 25 mm. San Bernandino Ranch, Mexican Boundary 

 Line, Arizona. 



A large number of shells and a few specimens preserved in alcohol 

 w^ere sent some time ago to the U. S. National Museum by Messrs 

 Mearns and Holzner of the International Boundary Commission. 

 Externally the shell closely resembles certain forms of Unio com- 

 planatics, but it is in general a smoother species, and has a more 

 delicate texture. Much as it differs from the ordinary Anodonta 



