1883.] 301 [Hyatt. 



with saddles in the young, have almost universally ventral lobes 

 in adults siphon above centre and more involute whorls. The 

 dorsal cones are in some species confined to the larval and adoles- 

 cent stages, disappearing in adults, whether the annular sutural 

 lobes disappear in adults is difficult to determine in fossils. Type, 

 Cen. (Naut.) intermedium, sp. Sow. D'Orb. Terr. Jurass. Ceph. 

 pi. 27. The resemblance of the Triassic forms to Barrandeoceras 

 is decisive for association in the same series, but there is as yet 

 no evidence that Cenoceras was directly derived from Barrande- 

 oceras. The frequent presence of longitudinal ridges in the 

 young and in some adults, the appearance of the annular lobes at 

 comparatively early stages, and the kidney-shaped whorls of the 

 larvae, also indicate derivation from Nephriticeras rather than 

 Barrandeoceras. We have, however, not yet found the inter- 

 mediate Carboniferous forms, and these, it must be remembered, 

 may prove to be gyroceran and arcuate shells belonging to the 

 common trunk or stock, but not necessarily to either of the gen- 

 era mentioned. Some Jurassic species have ridges and transverse 

 striae in the adult shells exactly as in the young of the existing 

 Nautilus. 



Cymatoceras, 1 nobis, includes Cretaceous species of the Ra- 

 diati, remarkable for their transverse costae. The abdomens are 

 rounded and the sides gibbous, though the whorls become com- 

 pressed in adults of some species. The sutures have large ventral 

 saddles, shallow lateral and dorsal lobes. The siphons are usually 

 sub-central. Annular lobes and cones are present in the larval 

 and adolescent stages, but disappear in adults. The young, as 

 noted first by D'Orbigny, are devoid of costae, these appearing 

 on the second, or even third whorl in some species. The ventral 

 sutures are distinctly lobed in the later larval stages, the saddles 

 developed later in the adolescent and adult stages. Doubtless 

 at still earlier stages than those observed by us, the suture pre- 

 sented the usual larval ventral saddles. Type, Cym. (Naut.) 

 pseudo-elegans, sp. D'Orb. Terr. Cretac. Ceph, pi. 8. 



Nautilus, 2 includes forms of the Jura, Cretaceous, Tertiary 



1 K.vp.a, a wave. 



2 Reexaminations of the young of this genus have satisfied the author of errors in 

 former views with regard to the funnels. The funnel of the second septum extends 

 to the opening of the coecum of the first septum on the ventral, but not on the dorsal 



