Braowiopopa. 
Glassia, Davidson. 
811 
1881. 
- (Plate 40, figs. 9-12.) 
Shells small, biconvex; elongate-ovate in outline; surface 
smooth. Umbo of the pedicle-valve not 
conspicuous; beak depressed. Structure 
of the deltidium and hinge as in Nucrz- 
ospira. Muscular impression consisting 
of two widely divergent, oval diductor 
scars, between which lies a broad 
adductor scar. 
Brachial valve with an internal sep- 
tum. The spiral cones have their bases 
toward the lateral margins of the shell 
and their apices at the center of the 
Fig 391 Glassia obovata, Sow- 
erby (sp.). Interior of the pedicle- 
valve. 
internal cavity; their position with reference to each other 
is, therefore, just the reverse of that in Merisrexia, Rerzta, 
etc. The cones are laterally compressed, and the ribbon 
makes but few volutions. The jugum originates as in Arrypa, 
Fic. 892. Brachidium of Glassia obovata, Sowerby (sp.). (DAvIpson.) 
is continuous, bending downward into the space between the 
cones and making a sharp angle at the point of union, which 
may be directed upward. 
Type, Glassia obovata, Sowerby (sp.). 
Distribution. Lower Silurian — Middle Devonian. 
63 
