white.] PALEONTOLOGY CEETACEOUS FOSSILS. 295 



of moderate size, tlie position of the posterior one of which is directly 

 beneath the beak, and both are directed somewhat forward. The poste- 

 rior one of the three is much the longest and diverges very obliquely 

 backward. Muscular impressions and pallia! line unknown. Surface 

 comparatively smooth, but marked with concentric lines and faint undu- 

 lations of growth. 



Length of the larger example, 35 millimeters ; height from base to 

 beaks, 23 millimeters. 



By the characteristics of the hinge of this shell, so far as they can be 

 ascertained, it appears to belong to the genus JBaroda Stoliczska, but 

 the shell is proportionally shorter than those of this genus usually are, 

 and its beaks are also more medially situated than is usual in Baroda. 

 Externally it has much the appearance of those Cretaceous forms which 

 are usually referred to Tellina. It resembles in outline the Tellina 

 (Palccomcera) incon&pima of Forbes, as figured by Stoliczska in vol. hi, 

 Palseontologia Indica, plate iv, fig. 8, but the character of the hinge, so 

 far as it has been seen, forbids the reference of this shell to Tellina. 



Position and locality. — Strata of the upper portion of the Fox Hills 

 Group ; at the mouth of the Saint Vrains, Northern Colorado, where it 

 was discovered by Mr. W. H. Holmes. 



Mactra? holmesi Meek. 



Plate 6, figs. 4 a, h, and c. 



Cyrena? holmesi Meek, 1875, Bull. Geol. and Geog. Surv. Terr., vol. 1 (2d ser.), No. 1, 



p. 45. 



" Shell under medium size, thin, transversely ovate or subtrigonal, 

 rather compressed ; anterior side shorter than the other and rounded in 

 outline; posterior moderately produced and subtruncated at the extrem- 

 ity ; basal margin transversely semiovate, its most prominent part being 

 antero-centrally; beaks somewhat depressed and placed about half-way 

 between the middle and the anterior ; dorsal margins forming a rather 

 long, nearly straight, or slightly convex, gentle slope behind the beaks, 

 and declining more abruptly in front, with a distinctly sinuous outline 

 just before the beaks ; surface ornamented with numerous fine, regular, 

 sharply defined concentric lines. 



" Length, 0.G2 inch ; height, 0.54 inch ; convexity, about 0.32 inch. 



" There are among the specimens apparently of this species quite a 

 variety of forms, produced, as I am inclined to believe, mainly at least, 

 by accidental distortion, though they may represent several distinct 

 species. The specimen from which the foregoing description and 

 measurements were derived presents the appearance of not having been 

 distorted, and, as may be seen by the measurements, is decidedly longer 

 than high. Others, however, agreeing exactly in surface-markings and 

 most other characters, have the length and height nearly equal, or the 

 latter even a little greater than the former. Some of the specimens also 

 differ from that taken as the type of the species in having the jjosterior 

 ambonal slopes prominent and subangular all the way from the beaks to 

 the posterior basal extremity, instead of only moderately convex. As 

 above intimated, however, all of the specimens departing decidedly from 

 the typical form show more or less indications of accidental distortion and 

 present precisely the same surface-markings as the typical specimen. 



"In regard to the generic relations of these shells, the specimens are 

 far from satisfactory, none of them showing the muscular or pallial im- 



