MOLLUSCA. CEPHALOPODA 



271 



whorl. Aperture with a sinus at the external margin. Sutures 

 with a simple wavy or angular lateral lobe, a lobe at the internal 

 margin (below the siph uncle) and a saddle at the external margin. 

 Siphuncle on the internal margin ; septal necks directed backwards. 

 Surface usually ornamented with transverse striae. Upper Devonian. 

 Ex. C. Icevigata. Clymenia is divided into Cyrtoclymenia, Oxy- 

 clymeiiia, Cymaclymenia, and Gonioclymenia. 



Mimoceras 1 . Shell discoidal ; the early whorls not in con- 

 tact, the later ones contiguous. Siphuncle at the external margin 2 . 

 Sutures very simple, concave on the sides of the whorls, with a 

 funnel-shaped external lobe. Devonian. Ex. M. compressum. 



Anarcestes. Shell with a wide umbilicus, and broad, rounded 

 external margin. Body-chamber long ; aperture with a deep ex- 

 ternal sinus. Sutures very simple ; the external lobe funnel-shaped 

 and not divided by a saddle ; lateral lobe very flat. Septal necks 

 long, directed backwards. Devonian. Ex. A. plebeius, Lower and 

 Middle Devonian. 



A B 



Fig. 110. Glyphioceras spharicum, from the Carboniferous Limestone. 

 The shell has been dissolved exposing the sutures. A, side view. 

 B, view showing aperture with the siphuncle at the external (upper) 

 margin. (From Woodward.) x f. 



Glyphioceras (fig. HO). Shell smooth or striated, whorls 

 generally large and embracing, with rounded external margin ; urn- 



1 This and the four following, with several other 

 formerly grouped together under the name Goniatites. 



2 In all the following genera the siphuncle has this position 



genera, were 



