522 MOLLUSCA 



SUB-KINGDOM VI 



narrow concave venter, and umbilicus small or closed. Sutures with prominent 

 ventral saddles undivided by ventral lobes in adult shells. Trias. 



Hercoglossa, Conrad (Enclimatoceras, Hyatt), (Fig. 1068). 

 Deeply involute, with sutures like those in Glyphioceratidae, but 

 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 lobes 

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

 lobes present. Jura. 



Aturia, Bronn (Fig. 1069). 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. 

 FIG. 1069. 



Aturia Aturi, Bast. sp. 



Miocene; Bordeaux. TTT "RVTTPFR ATTTA 



Shell broken open to 1V> ^TICERATIDA. 



show siphonal funnels. 



Cyrtoceracones, gyroceracones, and nautilicones having shells 



covered with more or less projecting bands of growth which often become sinuous or develop 

 into spout-like, spinous, or nodose prominences. In the more specialised shells these are apt 

 to be confined to the venter. TJie frills in the bands often form coarse longitudinal ridges. 

 Siphuncle tubular or slightly nummuloidal, and commonly ventrad of centre. 



Family 11. Halloceratidae. 



Orthoceracones and cyrtoceracones having depressed elliptical or subtrigonal section*, 

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

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

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

 either side springing 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. 



Cyrtoceracones and gyroceracones resembling Halloceratidae, but much larger, n-/tli 

 coarser crenulated bands, and often with rows of spout-like spinous processes which some- 

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

 than in Halloceratidae. 



Ryticeras, Hyatt (Rutoceras, Hyatt), Cophinoceras, Slrophiceras, Hyatt. Devonian. 



V. RHADINOCERATIDA. 



Cyrtoceracones, gyroceracones, and nautilicones having smooth or spinous longitudinal 

 ridges in the young, which 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. 



