SCHISTOCEKAS. 107 



the tliinl. The internal or dorsal lobes consist of a narrow and ])ointed 

 antisiphonal lobe, flanked on either side by a ])air of similar laterals, making 

 five internal lobes. 



]\Iiller and Gurley did not attempt to assign this species to its ])ropor 

 genus, and E. Haug" ascribed it to Agathkeras. The writer has, through 

 the kindness of Dr. Stuart Weller, examined the type specimen in the 

 paleoutologic collection of the Walker Museum, University of Chicago, and 

 has been able to determine it unquestionably as a Schistoceras, since in the 

 number and character of both external and internal lobes, fifteen in all, it 

 agrees with Hyatt's type specimen. 



It is most nearly related to Schistoceras iirissoiirien.se IVIiller and Faber, 

 but is more globose than that species and has a slightly narrower umbilicus, 

 which is only one-fifth of the total diameter of the shell, while in <S'. niissou- 

 riense it is nearly one-fourth. It also i-esembles S. hijatti in the narrow 

 umbilicus, but is more robust than that species and apparently lacks the 

 umbilical nodes. It ag-rees with S. hildretln in its robust form, but difters 

 in its narrower umbilicus. It is quite possible that all these species, <S'. 

 fuUonense, S. hyatti, and S. hilclretJii, may be only local varieties of the same 

 thing, in which case they would all fall under the synonymy of the latter 

 species. But not enough material is known at present to demonstrate a 

 gradation between them, and they are accordingly kept separated until the 

 discovery of sufficient material should warrant a union of all or part of 

 them in one species. 



Occurrence. — Upper Coal Measures, Fulton County, 111. Type in the 

 paleoutologic collection, Walker Museum, University of Chicago. 



Schistoceras hildrethi Morton. 



PL III, figs. 1 and 2. 



1836. Ainmo7i!tes hildrethi, S. G. Morton, Am. Jour. Sci., l.st series, Vol. XXIX. 



p. Ii9, PI. I, tig. 2-i; PI. XXVIII, tigs. i8, 50, 53, 54. 

 1898. Agathiceras hildrethi, E. Haug, Etudes sur les Goniatites, p. 105, PI. I, fig. 4(». 



Shell subglobose, involute; whorls highly arched, height being four- 

 fifths of their breadth; helmet-shaped, deeply embracing, concealing all but 

 the umbilical shoulder of the inner whorls, and indented by them to one- 

 third of its height. Umbilicus wide and deep, being nearly one-third of 



" Etudes' sur les Goniatites, pp. 33 ami 10.5. 



