1883.] 287 [Hyatt. 



ventral, and dorsal lobes, with small annular lobes. Siphon is 

 central or below the centre. Phi. (Naut.) gemmatura, sp. 

 Mojsis. Das Gehrig. Hallst. pt. 1, pi. 3. 



Pleuronautilus, Mojsis. Mediterr. Trias Prov. p. 273, in- 

 cludes a series of forms with more or less tuberculated, and 

 costated whorls, with sutures similar to the preceding. The 

 siphon is also below the centre. The young of one species, Pleu. 

 subgemmatum, as figured by Mojsisovics, ibid., pi. 85, is similar to 

 the adult of Phi. gemmatum, and appears to settle the question 

 of affinity. The sutures according to Mojsisovics vary from those 

 having ventral lobes to some having straight ventral sutures in 

 aged specimens. They have annular lobes. 



£Judoceratidae. 



This family includes forms in which the whorl in transverse 

 section is some modification of the fusiform outline. The abdo- 

 men may be flattened, but is never hollow. The siphons are 

 ventral, or between the venter and the centre. There is a 

 constant tendency to reduce the breadth of the dorsum, and 

 increase the venter. No sulcations or ridges are developed in 

 any genus. 



Eudoceras, Hall, Nat. Hist. N". Y., Yol. 5, pt. 2, supp. pi. 117, 

 includes straight shells of the Silurian and Devonian, with whorls 

 flattened, sides angular. The sutures have broad, ventral, and 

 dorsal lobes, the ventral lobe deepest ; and lateral saddles, which 

 are angular when the sides are angular, and more or less rounded 

 when the sides are rounded. The ventral and dorsal sides of the 

 whorl are equally convex, whorl in section being fusiform. Mus. 

 Geol. Surv. Albany. 



Tripteroceras, 1 nobis, has similar forms and sutures to the 

 preceding, but the lateral saddles are acute. The venter is flat- 

 tened, and broader than the dorsum, which forms the apex of the 

 subtriangular section. The siphon is ventral, and nummuloidal, 

 and the whorl arcuate in the young, though straight in the full 

 grown, and the aspect altogether distinct from the shells of the 

 preceding genus. The young are similar to the adults of Eudoc- 

 eras. Silurian and Devonian. Trip. (Orth.) hastatum, sp. Bill., 

 Rep. Prog. Geol. Surv. Can. 1853-56, p. 333, Mus. Geol. Surv. Can. 



1 Tpiirrrjp, a rubbing tool. 



