Logan.] The Invertebrates , Benton Group. 471 



JHortoniceras shoshonense Meek. Plate cm, figs. 1, 2. 



Mortoniceras shoshonense Meek, 1876, U. S. Geol. Surv. Terr., vol. ix, p. 449, 

 pi. vi, ff. 3a, c, 6b; Stanton, 1892, Bull. U. S. Geol. Surv., p. 179, pi. xliii, 

 ff. 1, 2. 



" Shell compressed-discoidal, with umbilicus apparently nearly 

 or quite twice as wide as the outer whorl ; volutions very nar- 

 row, with dorso-ventral and transverse diameters equal, and sec- 

 tion subquadrangular, those within scarcely one-sixth embraced 

 by the succeeding turn ; costse each mainly represented by two 

 nodes, the inner of which is low, compressed, and elongated so 

 as to extend from near the umbilical margin about half way 

 across the sides, while the outer near the peripheral margin are 

 more prominent, rounded, and directed laterally ; keel less promi- 

 nent than the row of compressed nodes on each side about half 

 way between it and the rounded nodes along the margins of the 

 periphery ; compressed nodes on the periphery of each inner 

 turn covered by the succeeding volution, the inner margin of 

 which is indented by the rounded lateral nodes of that next 

 within. Septa moderately approximate ; siphonal lobe oblong, 

 about once and a half as long as wide, with small, short, nearly 

 parallel, serrated terminal branches, and three or four very short, 

 digitate and simple branchlets and points on each side ; first 

 lateral sinus wider than the siphonal lobe, which it equals in 

 length, unequally bipartite at the anterior end, both divisions 

 being digitate, and the larger one on the siphonal side deeply bi- 

 fid ; first lateral lobe somewhat longer but narrower than the 

 siphonal, and having its terminal division deeply bifid, and its 

 lateral margins bearing a few very simple branchlets ; second 

 lateral sinus scarcely more than half as wide as the first, and 

 much shorter on the umbilical side, unequally bifid or trifid at 

 the end, with more or less sinuous margins ; second lateral lobe 

 only about half as long and wide as the first, and trilobate, with 

 the small middle division emarginate at the end ; third lateral 

 sinus a little shorter and narrower, and irregularly tridentate 

 at the end ; antisiphonal lobe about as long as the first lateral, 

 but narrower, with a few short, nearly simple, lateral divisions, 

 and a tridentate posterior extremity." 



