628 



MOLLUSCA 



PHYLUM VI 



are incoraplete internally, rising to saddles at the lines of Involution. Siphuncle 

 tubulär and small, and funnels comparatively sliort (Gümbel). 



1. Gyrtoclymenia (Fig. 1165), Oxyclymenia (Fig. 1167) Gümbel; Platyclymenia 



Hyatt. Devonian. 



Fio. 1166. 



§2. 



Conchs similar to tliose 

 of preceding genera, but sutures 

 liave two pairs of lateral saddles, 

 and tliere is a ventral lobe witli 

 ' a median saddle. 



Cymuclymenia (Fig. 1166), Sellaclymenia Gümbel. Devonian. 

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



Fig. 1165. 



Suture-line of Gyrtocly- 

 menia laevigata (Münst.). 



Butnre-line of Cymadymenüi 

 striata (Münst.). 



Fig. 1167. 



Oxyclymenia undulata (Münster). 

 Upper Devonian; Elbersreuth, 

 Fichtelgebirge. 



Fig. 1168. 



Gonioclymenia speciosa (Münst). Upper Devonian 

 Schübelhammer, Fichtelgebirge, i/o. 



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

 be either in part or wholly divided by marginals. 



Gonioclymenia (Fig. 1168), Gycloclymenia, Discoclymenia Gümbel; Gryptoclymenia 

 Hyatt ; Äcanthoclymenia Hyatt. Type Ä. (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 Geratites, between which there are no 

 sharp lines. 



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

 the Devonian and Carboniferous. 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. The 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 coUars. 



Family 1. Bactritidae Hyatt. 



Bactriticonesi and cyrtoceracones, usually compressed ellipitical in section, and c 

 necting through Protohactrites ivith the Nautiloidea. 



