vrarra.] PALEONTOLOGY CRETACEOUS FOSSILS. 295 



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

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

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

 bjickward. Muscular impressions and pallial line unknown. Surface 

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

 lations of growth. 



Length of the larger exami)le, 35 millimeters; height jBcom 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 Baroda 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 ai)pearance of those Cretaceous forms which 

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

 {ralccomcera) inconsincua of Forbes, as figured by Stoliczska in vol. iii, 

 Palceontologia 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 upi)er portion of the Fox Hills 

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

 was cliscovered by Mr. W. H. Holmes. 



Mactra? noL^iESi Meek. 



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



Cyrena? holmesi Meek, 1875, Bull. Geol. aucl Geog. Siirv. Terr., vol. 1 (2cl 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, Mith 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 w^ere derived x^resents the ai)pearance of not having been 

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

 than high. Others, however, agreeing exactly in surtace-markiugs 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 

 difier from that taken as the type of the species in ha^^ng the posterior 

 umbonal slopes ])romiiient and subangular all the w^ay from the beaks to 

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

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

 the lvi)ical 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 x)allial im- 



