628 



MOLLUSCA 



PHYLUM VI 



are incomplete internally, rising to saddles at the lines of involution. Siplumcle 

 tubular and small, and funnels comparatively short (Giimbel). 



§ 1. Cijrtoclymenia (Fig. 1165), Oxyclymenia (Fig. 1167) Giimbel; Platyclymenia 



Hyatt. Devonian. 



Fio. 1166. 



§ 2. Conchs similar to those 

 of preceding genera, but sutures 

 have two pairs of lateral saddles, 

 and there is a ventral lolje with 

 a median saddle. 



Cymaclymema (Fig. 1166), Sellaclymenia Giimbel. Devonian. 



§ 3. Conchs differ from preceding genera in that the sutures have deep undivided 



Fig. 1165. 



Suture-line of Cyrtody- 

 menia !(ui'i(iatri (Miinst.). 



Suture-line of Cymadymenm 

 striata (Miinst.). 



Fig. 1167. 



Oxydymenia undulata (Miinster). 

 Upper Devonian; Elber.sreutli, 



Fichteltrebirge. 



l-'ic;. 1168. 



Ooniodyncnia f:peeiom (Miinst.). Upper Devonian ; 

 Sehiibelhammer, Fichtelgebirge. 1/2- 



ventral lobes, and sometimes two pairs of lateral saddles are present. These last may 

 be either in part or AvlioUy divided by marginals. 



Gonioclymenia (Fig. 1168), Cycloclymenia, Discoclymenia Giimbel; Cryptoclymema 

 Hyatt ; Acanthochjmenia Hyatt. Type A. (Glymenia) neapolitana (Clarke). Devonian. 



Suborder B. EXTRASIPHONATA Zittel. 



The Extrasiphonata include straight, open-coiled and close-coiled forms, embracing 

 the old groups of Goniatites, Ammonites and Ceratites, between which there are no 

 sharp lines. 



The Goniatites are the oldest and most primitive Ammonoids, chiefly confined to 

 the Devonian and Carl:)oniferous. They are mostly small in size, distinguished from 

 the Clymeniidae by their external siphuncle, and from the rest of the Ammonoidea by 

 their simple septa. Tlie older Goniatites are retrosiphonate, and the aperture usually 

 has a ventral sinus. They grade over into Ceratites and Ammonites, the septa 

 becoming serrated or digitate, usually with an increase in the number of lobes, and 

 with the development of the forward-pointing siphonal collars. 



Family 1. Bactritidae Hyatt. 



Bactriticones and cyrtoceracones, usually compressed elliptical in sceiion, and con- 

 necting through Protobactrites with the Naxitiloidea. 



