CLASS V CEPHALOPODA 603 



Hercoglossa Conrad {EncUmatoceras Hyatt) (Fig. 1117). Deeply involute, with 

 sutures like those in Glyphioceratidae, l)ut the ventral saddle not divided by even the 

 shallow lobe usually found in that family. Annular lobes present 

 only in some species. Siphuncle small, centren or dorsad of centre. 

 Trias to Tertiary. 



Pseudonautilus Meek. Similar to Hercoglossa, but with lolies 

 on the venter, and two saddles on either side. Large annular 

 lobes present. Jura. 



Aturia, Bronn (Fig. 1118). Similar to Hercoglossa, but with 

 large siphuncle close to the dorsum from an early stage onward, 

 and funnels very long and larger than in any genus of Mesozoic 

 or Tertiary Nautiloids. Eocene and Miocene. 



IV. Ryticeratida Hyatt. 



Cyrtoceracones, gyroceracones and nautiliconcs having shells 

 covered with more or less x>'>'ojecting hands of growth which often Miocene; Bordeaux'. 

 become sinuous or develop into spout-like spinose, or nodose promi- ^}^^^^ broken open to 



■'..-' -^ ' T n 1 snow sipnonal tunnels. 



ncnces. In the more speciahsed shells these are apt to he confined, 



to the venter. The frills in the hands often form coarse longitudinal ridges. Siphuncle 



tubular or slightly nummuloidal, and commonly ventrad of centre. 



Family 11. Halloceratidae Hyatt. 



Orthoceracones and cyrtoceracones having depressed elliptical or suh-trigonal sections, 

 venter broader than the dorsum. Shell ivith closely set and frilled projecting bands of 

 growth, having large ring-like bands at intervals that sometimes expand so as to form 

 ivide collars. The highly specialised nautilicones may have a row of large nodes on 

 either side ^ringing from the bases of large spout-like spines. Siphuncle tubular, small, 

 and near the venter. 



Zitteloceras Hyatt. Cyrtoceracones of depressed elliptical section, the venter 

 narrower and more gibbous than the dorsum. The layers finely frilled and closely 

 set in the intervals between more prominent annular bands. Ordovician to Devonian. 



Halloceras Hyatt. Gyroceracones of sub-trigonal section, the venter broad and 

 dorsum sub-angular, with one row of large nodes at each of the ventro-lateral angles. 

 Devonian. 



Family 12. Ryticeratidae Hyatt. 



Cyrtoceracones and gyroceracones resembling Halloceratidae, but much larger, with 

 coarser crenulated bands, and often ivith roios of spout-like spinous processes ivhich some- 

 times form coarse longitudinal ridges. Siphuncle more or less nummuloidal, and larger 

 than in the Halloceratidae. 



Byticeras Hyatt {Rutoceras Hyatt), Gophinoceras, Strophiceras Hyatt. Devonian. 



V. Rhadinoceratida Hyatt. 



Cyrtoceracones, gyroceracones and nautilicones having smooth or spinous longitudinal 

 ridges in the young, lohich become large and fluted in some genera, but disappear in 

 others. Ridges more or less sporadically combined with fold-like annulations, thus 

 suggesting direct descent from the Kionoceratidae. 



Family 13. Rhadinoceratidae Hyatt. 



Primitive discoidal gyroceracones and nautilicones with stout volutions, circular or 

 depressed elliptical in section, but becoming reniform in later stages of nautilicones. 



