158 AMERICAN JOURNAL 



Observations. — A small, but beautiful species, not readily 

 confounded with any other; resembles Alas. caJmola, Lea, in 

 general form, but is less inflated, proportionally longer, and 

 is generally emarginate on the basal edge, besides being less 

 truncate on the posterior end. On the umbonial slope may 

 generally be observed several short, distinctly-impressed lines 

 often decussating; hence its name. Such lines are sometimes 

 seen in other species, but not often, and never so conspicuously 

 as in this. 



ALASMODO^^ rhombica, Anthony. — t. 12, f. 5. 



Description. — Shell smooth, quadrate or rhombic in form, 

 somewhat inflated, obtusely angulated behind, rounded before, 

 and nearly equilateral ; substance of the shell somewhat thin ; 

 beaks prominent, rugosely undulate at the tips and for some 

 distance below, occupying sometimes nearly half the first 

 growth ; epidermis olivaceous, faintly rayed, and with promi- 

 nent, somewhat crowded marks of growth; these marks of 

 growth are indicated by broad, darker bands, about four in 

 number on each valve ; anterior cicatrices rather deep and 

 distinct ; posterior cicatrices less deep and confluent ; nacre 

 deeply salmon-colored under the beaks, becoming fainter 

 towards the basal margin, where it is bluish-white and shin- 

 ing, but not iridescent. 



Dimensions. — Diameter finch; length 2 inches; breadth 1\ 

 inches. 



Habitat. — Michigan. 



My Cabinet. Cabinet of Hugh Cuming, London. Cabinet 

 of George W. Tryon, Jr. 



Observations. — This species cannot easily be mistaken for 

 any other, its short, quadrate form being sufficient to identify 

 it. In old specimens the epidermis is generally coarsely 

 striate and nearly black. It is less elongate, and not elliptical, 

 like A. edentula, Say, which often has the same colored nacre. 

 The ligament of this species is yellowish-brown, rather short 

 and slender. Among some twenty specimens now before me, 

 I find very little variation; not nearly so much as is usual in 

 this genus; and it is altogether a remarkably neat, pretty 

 species. 



Anodon subangulata, Anthony. — t. 13, f. 1. 



Description. — Shell broadly elliptical, very inequilateral, 

 rounded before and biangular behind ; substance of the shell 

 rather thick; epidermis greenish-j^ellow, the green predomi- 

 nating on the posterior half of the shell ; beaks slightly promi- 



