Hyatt.] 330 [April 4, 



those of the second list in the formations, up to the Lower Coal 

 Measures of Bigsby and Etheridge. 



[Dimerocerae.] 



Dimeroceras, 1 nobis, includes a single species, Dim. (Gon.) 

 mamilifer, sp. Sandb. Verst. Nass. pi. 5, fig. 5, which has rounded 

 first pair of saddles on the venter, rounded first lateral lobes, and 

 an additional pair of shallow, broad, angular, lateral lobes near the 

 umbilical shoulders, generated by the division of the magnosellarian 

 saddles. The ventral lobes are undivided and this species is 

 evidently a transitional from Brancoceras to Pericyclus. 



Pericyclus, Mojsis. Mediter. Trias. Pro v. p. 141, includes 

 two Carboniferous species which were designated by that author 

 without description. The spatulate first pair of saddles and the 

 additional, broad, angular, lateral lobes, which arise from div- 

 ision of the magnosellarian saddle give the sutures exactly the 

 aspect of those of Dimeroceras. The genus can be separated only 

 by the divided ventral lobes, and costations. Type, Peri. (Gon.) 

 princeps, DeKon. Anim. Foss. and Calc. Carbon, pi. 49, fig. 1. 



[Dimorphocerae.] 



Homoceras, 2 includes only the curious species (Gon.) calyx, 

 sp. Phill. Geol. York. pi. 20, fig. 22, 23. This has trapezoidal 

 whorls, like those of Gastrioceras, and sutures which are quite sim- 

 ilar to those of Glyphioceras. The form is, however, dwarfed with 

 sutures still more like those of Nomismoceras, which has sim- 

 ilar dwarfed forms. The siphonal saddles are small, the ventral 

 lobes broad, and open, the first saddles and lobes rounded, and the 

 magnosellarian saddles short, undivided, and rounded. The sut- 

 ures show the species to be in the same series as Nomismoceras, 

 but the highly depressed, trapezoidal form of the whorl obliges 

 us to separate it from that genus. Gon. mutabilis Phill. ibid, pi. 

 20, fig. 24, 25, not fig. 26, may also belong to this genus, but there 

 are no sutures as yet known. 



Nomismoceras, 2 nobis, includes a series of dwarfed forms 

 with compressed whorls, open umbilici, resembling in minature 

 the larger forms of the Prolecanites but differing from these 



1 Aijxep-r's- in two parts. 8 No'|uo"nos a c °i n - 



2 'OfxoVlike, 



