Hyatt.] 266 [April 4, 



NAUTILOIDEA. 



HOLOCHOANOIDA. 



Prochoanites. 

 Bathmoceras, Barr. Syst. Sil., Vol. 2, Tex. 1, p. 74, 3, p. 792, 

 supp. p. 92, equal Conoceras, Bronn. 



Nothoceras, Barr., ibid., Yol. 2, Tex. 1, p. 72. 

 Metachoanites. 

 Midoceratidae. 



Vaginoceras, nobis, type, (Orth.) multitubulatum, sp. Hall. 

 The funnels extend posteriorly beyond the next septum to that 

 from which they originated. The sheaths are very numerous, 

 and continuous, according to Whitfield, with the funnels. Endo- 

 siphon unknown. 



Endoceras, 1 Hall, Nat. Hist., N. Y., Vol. 1, p. 58. Funnels 

 extend posteriorly only from one septum to the next. Sheaths 

 not very numerous. Siphon not lined with an internal layer. 

 Endosiphon present, but not so thick walled, as in the genera 

 Sannionites or Piloceras, and generally destroyed by fossilization. 



Sannionites, Waldheim, Orcyto. Mosc, 1837, equal to Camer- 

 oceras, Conrad. Shell has only one large thick- walled sheath, in 

 connection, with the living chamber, not continuous with the 

 funnel of the last septum. The funnels close the intervals between 

 the septa as in Endoceras, but the siphon is lined by an inner, 

 thick, continuous layer of shell, which is composed apparently of 

 the unresorbecl upper parts of the successive sheaths. Endosiphon 

 is present, but only preserved in a fragmentary way, and often 

 absent in the fossils. 



Piloceras, Salter, as described by Dawson, Can. Nat. Vol. 10, 

 Similar to Sannionites in every essential characteristic, except 

 the walls of the siphon, which do not have the thick inner layer 

 present in that genus, and in the form. This is brevicone, and 

 arcuate, and often annulated, and has an enormous siphon with 

 compressed sheath, and endosiphon ; the latter usually destroyed. 



Cyrtocerina, Bill. Geol. Surv. Can., Pal. Fobs. Vol. 1, p. 178, is 

 similar in form to Piloceras, but the siphon is empty, in the few 



1 Colpoceras, Hall, Rep. Keg. State. Cab. 1850, p. 181, pi. 5, fig. 2, may be a siphon 

 of Endoceras as stated by Barrande, but we have neglected to study the type. 



