FOSSILS OP THE JURASSIC PERIOD. 287 



pi. 3, figs. 1 b iind c. The most general feature seems to be their small 

 size, although they differ in this respect, for while the majority of the speci- 

 mens range from half to thi-ee-fourths of an inch in length, other examples 

 are found attaining a length of an inch and a half 



It will be seen, by reference to the remarks of Messrs. Meek & Hayden 

 on this species, that they have met with all these various phases and varia- 

 tions among their specimens, although they speak of examples of much 

 larger size, where the attached valves are deep and strongly arcuate, with 

 large, strongly incurved beaks. These they term "normal forms" of the 

 variety, although it would seem that from some of their localities these 

 forms are nearly or quite absent, and that the flattened forms prevail. 

 Among the examples examined by us there are none of these "normal 

 forms", Ijut all are of the irregularly convex, the squarely truncate, or the 

 flattened forms above referred to ; and it seems to us that these forms are 

 much more likely to prove an entirely distinct species from the so-called 

 "normal forms" than that the)' are merely individual differences. In fact, 

 from the specimens beiore us, and from the figures above I'eferred to, it 

 appears that there is but little reason for considering the forms under con- 

 sideration as belonging to any other genus than Ostrea ; while those 

 referred to as "normal forms" are unquestionably true Gryphaa* 



In the flattened and almost wholly attached exaniples, the form and 

 characters are so exactly similar to Ostrea congesta Conrad, from the Creta- 

 ceous formations, that it is nearly or quite impossible to say wherein they 

 differ, except, perhaps, that they are not so gregarious or so densely packed 

 together as that species often is. 



Formation and locality.-— In shaly limestone of Jurassic age, at Sheep 

 Creek, Uinta Range, Utah, associated with Camptonectes heUistriatus, Penta- 

 crinites asteriscus, &c.; and on Ashley Creek, Uinta Range, associated with 

 Camptonectes? cxtenuatiis, Bellemnites densa, &c. Collected by S. F. Em- 

 mons, esq. 



* Since the iibove paragraph was wiitteu, Dr. 0. A. White has described these 

 small shallow torins under the uaine Ostrea dtrigilecula (see Pal. Rep. Geograph. and 

 Geol. Surv. and Expl. West of 100th Merid., Lieut. Wheeler in charge, by C A .White, 

 p. 1G3, pi. xiii, fig. 3). 



