STANTON.] OSTREIDiE. 61 



erally having an irregularly subovate marginal outline, often much 

 longer than broad, but sometimes shorter than broad. Larger valve 

 capacious, scaphoid, arcuate, more or less distinctly lobed, the poste- 

 rior lobe occasionally somewhat wing-like; test rather thick; umbo 

 large, prominent, and incurved, or flattened and short; scar of attach- 

 ment small or wanting; surface sometimes distinctly lamellose, but 

 generally somewhat smooth, although marked by concentric lines of 

 growth. 



" Upper valve nearly flat, moderately thick in the umbonal region; 

 hinge Hue well defined, straight; area distinct; ligamental groove 

 small; inner surface smooth, more or less distinctly crenulated at the 

 lateral edges; outer surface marked by numerous concentric, imbricat- 

 ing lines of growth, and sometimes also by faint, impressed radiating 

 stride. 



"The collections contain numerous examples of this widely known 

 species, none of which, however, are of so large a size as are some of 

 those figured by Roemer, Conrad, and others. In selecting examples 

 for illustration I have chosen representatives of two extremes of form 

 from among others of all intermediate gradations. Mr. Conrad states 

 (loc. cit.) that there are two distinct varietal types of this species, one 

 of which resembles G. vesicularis Lamarck, and which was the typical 

 form described and figured by Dr. Morton ; and the other he designates 

 as var. navia. The collections under examination, however, although 

 they contain representatives of the two forms referred to by Mr. Con- 

 rad, seem to indicate no constancy of separate varietal character, 

 either of those forms or any others. 



" The largest specimens in the collections have a length of only about 

 37 millimeters from the umbo to the basal margin, which is consider- 

 ably less than that of some examples reported by other authors." 



It is with much hesitation that I propose a new name for this form, 

 because as a rule species of the Ostreidge are difficult to define, and 

 because I do not wish to add to the confusion that has long prevailed 

 concerning Gryphcca pitcheri. 1 The latter species is very abundaut in, 

 and has been regarded as characteristic of, the Comanche series, or 

 Lower Cretaceous, of Texas and adjacent regions. 



The form now under consideration occurs in great numbers in the 

 lower part of the Upper Cretaceous shales in southeastern Utah and 

 adjacent portions of Colorado, Arizona, and New Mexico, where it is 

 associated with characteristic fossils of the Colorado formation, such 

 as Inoceramus labiatiis, Inoceramus fragilis, and many others. It is 

 reported from this horizon at many localities by Br. Newberry. 2 



It was collected by Mr. CD. Walcott about 350 feet above the base 

 of his Cretaceous section in Upper Kanab valley, Utah, and the speci- 



1 For discussions of Gryphcea pitcheri and its varieties see R. T. Hill in Ann. Rept. Arkansas Geol. 

 Sur., 1888, Vol. n, pp. 168-174, and Bull. No. 4, Tex. Geol. Sur., p. 4, and Jules Marcou, Am. Geologist, 

 Vol. in, p. 188. 



2 Macomb's Expl. Exped. Geol. Rept., pp. 33, 52, 71, 87, 107, etc. 



