WHITE ON NEW INVERTEBRATES. 709 



examples larger than this were discovered, but it is possible that those 

 obtained are under full adult size. 



Position and locality, — Laranaie Group, about 400 feet above its base; 

 Danforth Hills, near White Kiver ludian agency, Northwestern Colorado. 



Genus ANODONTA Cuvier. 



Anodonta parallela (sp. nov.). 



Shell transversely much elongate, oblong or semi-elliptical in marginal 

 outline ; valves gently convex, apparently a little more so near the 

 front than elsewhere ; beaks situated about two-sevenths the length of 

 the shell from the front, depressed, the elevation of the umbonal re- 

 gion being hardly perceptible; hinge-line long; the whole dorsal border 

 nearly straight ; both anterior and posterior borders regularly rounded; 

 that of the posterior being a little more abruptly rounded than the 

 front; base nearly straight, or very slightly emargiuate along or a little 

 in front of the middle. Test thin ; surface smooth or marked only by 

 the ordinary lines of growth and one or two faint ridges running from 

 the beaks to the postero-dorsal margin. 



Length 63 millimeters ; breadth 20 millimeters. 



The extraordinary length of this shell compared with its width is an 

 unusual feature in this genus ; but all the other characteristics of the 

 species, so far as they can be observed on the specimens yet discovered, 

 indicate it to be a true Anodonta,^ and its immediate associates are also 

 all fresh-water shells. Only two examples have been discovered, both 

 imperfect ; but together they show all the essential characteristics of the 

 species. Notwithstanding its unusually elongate form, the character 

 of the test and its edentate hinge apparently leave no doubt as to its 

 generic character as here indicated. 



Position and locality. — Laramie Group ; Valley of Crow Creek, North- 

 ern Colorado, about 10 miles above the confluence of the creek with 

 South Platte Eiver. 



Genus UNIO Eetzius. 



Unio goniambonatus (sp. nov.). 



Shell of medium size, transversely elongated, subtrihedral iu mar- 

 ginal outline, being rapidly narrowed posteriorly from the anterior i^or- 

 tion; moderately gibbous, most so a little in front of its mid-length and 

 above its mid-height; test somewhat thick; beaks placed near the 

 anterior end, moderately depressed ; umbones slightly raised above the 

 hinge-line ; umbonal ridge distinct, angular, and so prominent as to 

 produce a flattened or even slightly concave space between it and the 

 hinge-margin, giving the whole back of the shell a broadly flattened as- 

 pect; front margin regularly rounded from beneath the beaks to the basal 

 margin, which latter margin is nearly straight or only slightly convex, 

 especially behind the anterior third of its length ; posterobasal margin 

 narrowly rounded to the postero-dorsal margin, which meets the former 



