74 PALEONTOLOGY. 



Peoductus semistriatus, Meek. 



Plate 7, figs. 8, 8 a. 



Productus semistriatus, Meek (18G0), Proceed. Acad. Nat. Sci., XII, 309; and (187G) in 

 Col. Simpson's Report Expl. across tbeGreatBasiu of Utah, 347, pi. I, figs.7 «,&. 



Compare Productus Chandlessii, Derby (1874), Bull. Cornell Univ., I, 51, pi. iv, figs. 

 1-16, and pi. vi, fig. I. 



Sliell rather under medium size, very gibbous, greatest breadtli on tlie 

 liino-e-line, wliicli is nearly twice the length, measuring from the beak direct 

 to the anterior slope, but only a little more than half as great as the length 

 of the ventral valve, measuring over its curve. Ventral valve extremely 

 convex, strongly arched, and much produced in front, sometimes provided 

 with a very shallow mesial sinus ; beak gibbous and distinctly incurved, so 

 as to pass within the cardinal margin ; ears triangular, strongly vaulted, 

 and abruptl}^ separated from the vertical sides of the gibbous umbonal 

 region by a rounded, undefined sulcus, which is continued from the beak 

 to the lateral margins, to tlie outline of which it imparts a more or less 

 sinuous character in front of each ear ; surface of the visceral region marked 

 by small concentric wrinkles extending upon the ears, and crossed by 

 nnmerous rather fine longitudinal striae, or costae, that become suddenly 

 obsolete on all of the anterior and lateral slopes from above (behind) the 

 middle : these parts of the surface being merely marked with obscure lines 

 of growth and strong, regularly-scattered spine-bases, from each of which 

 there is sometimes a very obscure, undefined ridge extending downward to 

 or toward the free margin. Similar spine-bases are also seen over other parts 

 of the surface, including the ears ; though they nowhere arise from tuber- 

 cles. Dorsal valve unknown. 



Length, measuring direct from the umbo to the anterior slope, 0.83 

 inch; measuring over the curve of the ventral valve from the beak to> 

 the anterior margin, 2.25 inches; breadth to the extremities of the ears, 

 about 1.34 inches ; breadth of most gibbous part of umbonal region, 0.90 

 inch; number of longtitudinal strias on the posterior half of the ventral 

 valve, in the space of 0.10 inch, 3. 



This seems to be a well-marked species, which is peculiar in having 

 well-defined longitudinal striae and moderately distinct transverse wrinkles 



