Logan.] The Invertebrates, Benton Group. 473 



lateral sinus hardly half as long or wide as the second, and 

 merely faintly bilobate at the end ; third lateral lobe a little 

 oblique, simple and smaller than one of the principal terminal 

 digitations of the first lateral lobe. Greatest diameter, 1.10 

 inches; convexity, about .26 inch." 



This form occurs in both the Fort Benton limestone and the 

 Septaria horizons. In the former it occurs as impressions in 

 the rock ; in the latter, as casts in the calcareous nodules which 

 are in the Blue Hills shales. 



Scapltites I a r ire for mis M. & H. Plate civ, fig. 2. 



Scaphites larvceformis M. & H., 1856, Proc. Acad. Nat. Sci. Phil., p. 58; 

 Meek, 1876, U. S. Geol. Surv. Terr., vol ix, p. 418, pi. vi, ff. 6a, b, c; 

 Stanton, 1892, Bull. U. S. Geol. Surv. No. 106, p. 182, pi. xliv, f. 2. 



Revised description: "Shell small, transversely subovate, 

 compressed, evenly rounded on the periphery ; volutions slender, 

 nearly round, the inner or coiled ones forming only a very 

 small part of the entire shell, and so closely involuted as to 

 leave only a very small umbilical pit ; extended body portion 

 rather long, slender and straight to the recurvature, thence con- 

 tinued backward until it comes nearly in contact with coiled 

 inner volutions ; aperture apparently circular ; surface orna- 

 mented by small costse, which pass from the inner side of the 

 volutions to about half way across their lateral surfaces, where 

 they swell into small obscure, transversely elongated nodes, and 

 then branch each into two or three small linear ribs, all of 

 which pass straight over the periphery. Septa moderately 

 simple, having two main lateral lobes on each side, all of 

 which are only moderately divided. The siphonal lobe is 

 longer than wide, and has two very small, short, nearly parallel, 

 obscurely bifid terminal divisions, with a more oblique, some- 

 what similar branch on each side above. The first lateral sinus 

 is wider than the siphonal lobe, and nearly as long, with its 

 extremity deeply divided by a slender, obscurely trifid, auxil- 

 iary lobe, into very unequal, more or less sinuous, and ob- 

 tusely digitate branches. First lateral lobe about half as wide 

 as the siphonal, but somewhat shorter, and bearing two very 

 small terminal divisions similar to those of the siphonal lobe. 



