134 PALEONTOLOGY. 



the beaks to the posterior basal angle. Surface ornamented with small, 

 very regular, concentric costse, which terminate abruptly on the posterior 

 umbonal ridge of each valve, or are only continued on the compressed pos- 

 terior dorsal region above the angle as fine lines of growth. 



Length, 0.44 inch; height, about 0.36 inch; convexity, about 0.15 inch. 



This shell seems to agree very closely in outline and surface-markings 

 with the published figures of Miinster's species, and I am inclined to believe 

 it the same; though it is quite as probable that a good series of specimens 

 would show specific differences separating it from that shell. As I have 

 only seen a single imperfect specimen, however, and that presents no relia- 

 ble characters by which it can be distinguished, I refer it with doubt to M. 

 lineata. I should remark here that its costse are much more strongly marked 

 than on Miinster's species, as illustrated by Dr. Laube, in his work on the 

 St. Cassian Fossils, but in this respect our specimens agree exactly with 

 Goldfuss' figures of that species. 



Locality and position. — Weber Cation, Wasatch Range, Utah; from above 

 "quarry rock". In Europe, M. lineata occurs in the St. Cassian beds; but 

 the shell here described appears to occupy a higher position (in the Jurassic 

 seriesj if its exact position in the section was accurately determined. 



AROID^. 



Genus CUCULL^A, Lamarck. 

 CucuLL^A Hagubi, Meek. 

 Platel2, figs. 1, la, 16. 

 Compare CueuUcea concinna, Phillips (1835), Geol. Yorks., 160, pi. v, fig. 9. 



Shell small, oblong-subrhomboidal in outline, about once and a half as 

 long as high, and rather gibbous in the central region ; posteriorly a little 

 obliquely truncated above, and obtusely-subangular and most prominent at 

 its connection with the base below ; base nearly straight and parallel to the 

 cardinal margin along the middle, and rounding up rather more gradually 

 in front than behind ; anterior margin compressed, convex in outline, and 

 connecting with the hinge above at an angle of about 98° ; hinge-line less 

 than the greatest length of the valves ; beaks rather prominent, gibbous, 



