CLASS V 



CEPHALOPODA 



597 



ventrally. Siphuiicle with fuimels only in the young, the collars in ephebic stages 

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

 Glossoceras Barr. Known only by gerontic living Chambers, 

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

 and lateral crests. Silurian. 



Volborthella Schmidt. * Minute orthoceracones with conical 

 septa, small siphuncle, perfectly piain 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, known only hy their gerontic 

 living chamherSy and aßnities therefore uncertain. They are globular 

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

 approximately dumh-hell shaped apertures. 



Wv 



Fio. 1106. 



Äscoceras mamchrium 

 Lindström. Silurian ; 

 Gotland. 1/2. (Re- 

 stored after Lindström.) 



Fig. 1107. 



Äscoceras bohcmicuvi Barr. iSilurian (Etage E) ; Kozorz, Bohemia. A, 

 Specimeu with shell partially preserved. B, Mould of living Chamber detached 

 from preceding portion. C, Longitudinal section. 7t', Living Chamber; c 1-4, 

 Camerae ; l 1-4, Saddles contracting the living Chamber, i/j (after Barrande). 



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

 gerontic sigmoidal septa. Silurian. 



Billingsites Hyatt. Aperture without hyponomic sinus. Gerontic living Chamber 

 partly fiUed by dorsal sigmoidal saddles as in Äscoceras, but septa complete on the 

 ventral side. Silurian. 



Suborder C. SCHISTOCHOANITES Hyatt. 



Funnels usually more or less imperfecta present on the internal side, and ahscnt or 

 split on the outer side. 



The typical form of the suborder is Conoceras Bronn. 



Gyrtocerina Billiugs. Breviconic cyrtoceracones. Siphuncle large, on the 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, 



