1883.] 281 [Hyatt. 



Streptoceras, Bill. Geol. Surv. Can. 1866, Antic. Foss. p. 88, 

 fig. 28, appears to be identical with Acleistoceras, but the aper- 

 tures are more like those of Maelonoceras. The form, however, is 

 very distinct from both of these genera, and the living chambers 

 one-third of the length of the whorl. This would not be impor- 

 tant in most series, but in this one it is an extraordinary variation, 

 and is perils an indication of essential differences. Mus. Geol. 

 Surv. Can. 



Cranoceras, 1 nobis, includes arcuate Silurian species, which 

 have depressed elliptical whorl in section, and are very closely 

 allied to Maelonoceras. Tl e sutures straight, or with dorsal and 

 ventral saddles, and lateral lobes. The siphon is near venter. 

 In the later stages of more curved forms slight dorsal lobes are 

 developed. Cran. (Cyrt.) hospitale, sp. Barr. pi. 151, nigrum, 

 ibid., pi. 127, Turn us, ibid., pi. 483, 484, of the Silurian connect 

 intimately with the Devonian type (Cyrt.), depressum, sp. Goldf., 

 D'Arch. et Vern. Trans. Geol., Soc. Vol. 6, pi. 29, fig. 1, Schultze 

 Coll. Mus. Comp Zool. The type has very short living chamber, 

 and aperture very similar to that of Mael. praematurum, but 

 wider transversely and with deep ventral sinus, as in some species 

 of Acleistoceras. The general form, aspect, size, and siphon as in 

 Turnus. 



Naedyceras, 2 nobis, includes forms with whorls in section 

 subtriangular, the dorsum broad and flat, the abdomen depressed, 

 and subangular. The siphon is near the venter and nummu- 

 loidal. The sutures as in Cranoceras, but dorsal lobe more pro- 

 nounced, no annular lobes, and no imprassed zone on the dorsum. 

 The genus includes Naed. (Cyrt.) anormale, sp. Barr. pi. 139, 

 (N"aut.) vetustum, ibid., pi. 35, in the Silurian, and also a series of 

 degraded arcuate, and gyroceran, Devonian forms which show 

 degeneration in their trochoceran mode of growth. They are 

 also recognized by Professor Hall, as having marks of nautilian 

 affinities. These characteristics could only have been derived from 

 gyroceran ancestors, like Naed. vetustum. Type, Naed. (Troch.) 



Eugenium, sp. Hall, Nat. Hist., N. Y., Yol. 5,] pt. 2, pi. 58, 59, 



Mus. Geol. Surv., Albany. 



1 Kpavos, a helmet. 



2 Nt]6vs, the belly. 



