EXPLORATIONS ACROSS THE GREAT BASIN OF UTAH. 



LAMELLIBRANCHIATA. 



Genus AVICULOPECTEN, McCoy. 



Aviculopecten Utahensis, Meek. 



, apparently nearly equi- 

 ^r; ears small, subequal, 



thread-like, concentric- lines, scarcely visible without the aid of a lens; light valve 

 smooth, or only marked 1>\ line concentric- stria;. 



Length, about 1.10 inches; breadth, 1.20 inches; length of hinge, 0.57 inch. 



Sometimes the radiating cost* are nearly equal, but usually there are two, three, 

 four or more smaller ones between each two of the larger. The smaller costa? gene- 

 rally die out or coalesce with each other or the larger ones before reaching the beak. 

 They are all usually obsolete on the lateral margin's, and always wanting on the ears, 

 which are only marked by fine, closelv-arranged, concentric strife. 



Locality aud position.— Snmn.it Spring Pass, divide between Long and Ruby Val- 

 leys; latitude, S\) z 33', longitude, 115° 12' west. Probably Upper Carboniferous. 



CEPHALAPODA. 

 Genus ORTHOCERAS, Auct. 

 Orthoceras baculum, Meek. 



Plate 1, fig. 10, a. b. 

 Orthoceras baculum, Meek (July, I860), Proceed. Acad. Nat. Sci. Philad., XII, 310. 



Shell rather small, elongate-conical; section very nearly circular near the smal- 

 ler end, and slightly oval toward the aperture ; sides diverging from the -apex at an 

 angle of 8°; septa not oblique, distinctly concave on the anterior side, separated by 

 spaces equal to one-fifth their own greater transverse diameter; siphuncle rounded, 

 nearly but not quite central, a little less than one-sixth the diameter of the shell; sur- 

 face apparently smooth. 



t The only specimen of this species in the collection is a fragment, imperfect at 

 both extremities, and about two inches in length, with a diameter at the smaller end 

 of 0.47 inch. Although it retains no surface-markings, there may be fine lines of 

 growth on well-preserved specimens. 



In form and proportions this shell is quite similar to two or three species described 

 by de Koninck from the Carboniferous rocks of Belgium. It differs, however, from 

 his 0. Goldfussianum (pi. xliii, figs. 3 and 4, Animaux fossiles), which it seems to resem- 



