516 MOLLUSCA SUB-KINGDOM VI 
Aphragmites, Barr. Only gerontie living chambers known; these are similar to 
those of Ascoceras, but have no internal sigmoidal dorsal saddles, Silurian. 
Ascoceras, Barr. (Figs. 1057, 1058). Gerontic living chambers 
internally contracted by the formation of large sigmoidal saddles, 
and septa more or less incomplete ventrally. Siphuncle with 
funnels only in the young, the collars in ephebie 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 aperture has dorsal 
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 Cam- 
brian; Finland, Esthonia. St. John’s Group; Nova Scotia. 
A B Cc 
—. 

Fic. 1058, 
7 or 
Fie. 1057. Ascoceras bohemicum, Barr. Silurian (Btage E); Kozorz, Bohemia. 4, 
Ascoceras manubrium, Specimen with shell partially preserved. LB, Cast of living chamber detached 
Lindstrom. Silurian ; from preceding portion. C, Longitudinal section. w, Living chamber ; 
Gottland. = 1/y, (Re- c 1-4, Camerae; / 1-4, Saddles contracting the living chamber. 1/; (after 
stored after Lindstrom.) * Barrande). 
Family 2. Mesoceratidae. 
Depressed elliptical cyrtoceracones, known only by their gerontic living chambers, and 
affinities therefore uncertain. They are globular at this stage, and have highly contracted, 
transversely elongated, and approximately dwmb-bell-shaped apertures. 
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, 
Sub-Order C. SQGHISTOCHOANITES. Hyatt. 
Funnels usually more or less imperfect, present on the internal side, and absent or 
split on the outer side. 
This group will be better understood after the publication of Professor W. B. 
