SUB-OKI >K K K OYBTOCHOANITES 5t7 



ma. Sutures slightly inllertr.l, with taint ventral lol -.- ; annular ].!..- pres.-nt. 

 \'< ilut ions sub-globose, a n< 1 umbilical perforation comparatively large. 

 Sijiliuncle centren in the apical camera, but later becoming v-nlral 

 of centre. Tertiary (?) to Recent. 



Sub-Order E. CYRTOCHOANITES. Hyatt. 



Shells varying from orthoceracones to nautilicones, none of them 

 liinlilij ornamented, although some are annulated or costated, am/ in 

 rare cases slightly nodose. Sutures as a rule simpler than in Ortho- 

 choanites. Siphuncle varies exceedingly, passing from tubular in the 

 young and even in the full-grown of primitive forms to highly nummu- 

 loidal in the adults of specialised genera, or again in some groups 

 nfn/niiKi constantly its primitive character. The funnels, however, 

 are as a rule bent outward or crumpled, and generally short. 



FIG. lOTO. 



T A wr-TfvsTTmnxrATA Nautilus ' 



1. A^LLOSIPHONATA. Titlioni.-m : 



Stramberg, Moravia. 



Mostly orthoceracones and cyrtoceracones, with a few gyroceracones 



and very rarely nautilicones, the last-named being invariably discoidal. Apertures 

 constantly open. Siphuncle may be empty, but organic deposits when present always 

 gathered about or encrusting the funnels as hollow or solid internal rings. Deposits 

 sometimes sufficient to form more or less annulated endosiphuncles, the rings being opposite 

 the camerae, alternating with the septa, and extending outwardly. 



Family 1. Loxoceratidae. 



Smooth orthoceracones and cyrtoceracones similar to Orthoceratidae, but siphunch 

 distinctly nummuloidal, and funnels very short and crumpled. Deposits not uncommon, 

 but irregular, and only irregular endosiphuncles occasionally formed. 



Loxoceras, M'Coy (Sactoceras, Hyatt). Mostly orthoceracones, circular or elliptical 

 in section. Siphuncle supposed to be tubular in the y<nmg, but highly nummuloidal 

 in later stages, centren or near the centre. Septa invariably single, and camerae 

 empty. Ordovician to Carboniferous. 



Campyloceras, M'Coy (Aploceras, Hyatt). Breviconic cyrtoceracmie-, or orthocera- 

 cones with smooth or finely ridged shells, circular or depressed elliptical in section. 

 Siphuncle centren or ventrad of centre. Carboniferous. 



Family -2. Uranoceratidae. 



Cyrtoceracones, gyroceracones, and nautilicones with stout volutions. Siphuncle in 

 primitive forms highly nummuloi<ll, hut invariably empty ; in nautilicones it ////* /< 

 nummuloidal segments, and is uniformly ventrad of centre, but not near f/i> venter. 

 Sutures with ventral saddles, lateral lobes, and also dorsal saddles in primitive forms as 

 well as the young of all shells. !"</'//>/ and dorsal lobes arise subsequently in tin- 

 ontogeny of nautilicones. 



Uranoceras, Hyatt. Stout, mdre or less breviconic cyrtoceracones, compressed 

 elliptical or sub-quadrangular in section. Sutures with broad ventral saddles, lateral 

 and dorsal lobes. Siphuncle large, nummuloidal, centren or ventrad of cent re. 

 Devonian and Carboniferous. 



Gigantoceras, gen. nov. Gyroceracones similar to the preceding, but having longer 

 living chambers and more compressed volutions. Includes the largest known Nau- 

 tiloid shells. Type G. (Gyroc.) inelegans, Meek sp. Silurian. 



