1883.] 291 [Hyatt. 



adults by quadragonal whorls. The dorsal saddles are retained, 

 and though dorsal lobes are formed in the nautilian species, these 

 are often subdivided by a minute saddle. Siphon is above the 

 centre. 



Trigonoceras, 1 McCoy, Carb. Foss. Ireland, 1844, p. 9, Nautil- 

 oceras D'Orb., Prod. Pal. p. 110, is a synonym. Trig. (Gyr.) para- 

 doxicum, DeKon. Anim. Foss., and Gyr. aigoceras, ibid., 

 D'Orbigny's type are the same species, the latter being the young 

 of the former. The young have lateral costae until a late stage 

 of growth. The abdomen is hollow, the junction with the sides 

 angular, the sides themselves gibbous, and the whorl in section 

 consequently shield-shaped, the dorsum forming the acute apex. 

 The adults retain the form, but lose the costae. The siphon is 

 above the centre. The sutures have broad dorsal lobes, saddles 

 at the angles of the abdomen and sides, lateral lobes and dorsal 

 saddles. This genus seems to be directly transitional to Apsido- 

 ceras, but we have not yet seen the young. The similarities of 

 this genus and the hollow abdomened forms of the Tribolocerati- 

 dae have been frequently noticed by authors, but we do not regard 

 them as indicating a close genetic connection. 2 



Stroboceras, nobis, includes Carboniferous species which are 

 similar to Trigonoceras in their larvae, but elevate the abdomen 

 develop two pairs of lateral ridges, and have gibbous inner umbilical 

 shoulders so that the dorsum becomes broader than the abdomen, 

 and decidedly gibbous. The sutures have broad abdominal sad- 

 dles, small acute saddles at the lateral ridges, narrow lobes on 

 either side, broad lateral saddles on the swollen or gibbous part 

 of the whorl, and small, sub-acute, dorsal lobes. Apertures are 

 contracted laterally, and dumb-bell shaped. Siphon is half way 

 from the centre to the venter. Type, Strob. (Discites) Hartii. 

 sp. Daws. Acad. Geol. Ed. 3, p. 311, fig. 125, Mus. McGill College. 



Trematodiscus, 3 Meek, was finally established by this author 

 in his Invert. Pal. U. S. Geol. Surv. Hayden, Vol. 9, p. 491, with 

 Trem. (ISTaut.) stygialis of the Carboniferous, DeKon. Anim. Foss., 

 pi. 45, fig. 11 as th° type. The larvae are at first stage observed 



1 Srpoftos , a vortex. 



2 See p. 293, Triboloceratidae. 



3 We propose to change this name to Trematoceras since it was used by Hackel in 

 1860.for the Radiolaria, and by Eichwald for Bactrites. 



