CLASS V 



CEPHALOPODA 



)97 



ventrally. Sipliuncle with funnels only in the young, the collars in ephebic stages 

 becoming nummuloidal and often incomplete in old age. Aperture open. Silurian. 



Glossoceras Barr. Known only by gerontic living chambers, 

 which are like those of Ascoceras, except that the aperture has dorsal 

 f^^^p' and lateral crests. Silurian. 



Volborthella Schmidt. Minute orthoceracones with conical 

 septa, small siphuncle, perfectly plain upon the surface of the septa. 

 Living chamber flaring and uncontracted. Lower Cambrian ; 

 Finland, Esthonia. St. John Group ; Nova Scotia. 



Family 2. Mesoceratidae Hyatt. 



Depressed elliptical cyrtoceracones, hnoion only hy their gerontic 

 living chavibers, and affinities therefore uncertain. They are globular 

 at this stage, and have highly contracted, transversely elongated, and 

 approximately dumb-bell shaped apertures. 



^, 



FiC!. 1106. 



Ascoceras inanuhrium 

 Linilstrom. Silurian ; 

 Gotland. i/.i. (Re- 

 stored after Lindstrom.) 



Fig. 1107. 



Ascoceras bohemicum Barr. Silurian (Etage E) ; Kozorz, Bohemia. A, 

 Specimen with shell partially preserved. ]J, Mould of living chamber detached 

 from preceding portion. C, Longitudinal section, w, Living chamber ; c 1-4, 

 Camerae ; I 1-4, Saddles contracting the living chamber, i/i (after Barrande). 



Mesoceras Barr. Aperture with very shallow hyponomic sinus. No internal 

 gerontic sigmoidal septa. Silurian. 



Billingsites Hyatt. Aperture without hyponomic sinus. Gerontic living chamber 

 partly filled by dorsal sigmoidal saddles as in Ascoceras, but septa complete on the 

 ventral side. Silurian. 



Suborder C. SCHISTOCHOANITES Hyatt. 



Funnels usually more or less imperfect, present on the internal side, cmd absent or 

 split on the outer side. 



The typical form of the suborder is Conoceras Bronn. 



Gyrfocerina Billings. Breviconic cyrtoceracones. Siphuncle large, on tlie concave 

 side and empty, but having internal ridges alternating with septa of the camerae. 

 These ridges appear to indicate affinity with Conoceras. Ordovician. 



Conoceras Bronn {Bathmoceras Barr.) (Fig. 1108). Breviconic orthoceracones, 



