152 
PALEONTOLOGY OF NEW YORK. 
Genus GLASSIA, Davidson. 1881. 
1849. Atrypa, Sowerby. Silurian System, pi. viii, fig. 9. 
1859. Athyrisf Salter. Siluria, second ed., p. 542, pi. xxii, fig. 16. 
1867. Athyns, Davidson. British Silurian Brachiopoda, p. 121, pi. xii, fig. 19; pi. xiii, figs. 5, a. 
1881. Glassia, Davidson. Geological Magazine, new series, vol. viii. 
1882. Glassia, Davidson. British Devonian and Silurian Brachiopoda Supplement, p. 38, pi. i, figs. 
10-14; pji. 116-120, pi. vii, figs. 9-20. 
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 Nucleospira. Muscular impression consisting of 
two widely divergent, oval diductor scars, between which lies a broad ad¬ 
ductor scar. 
Fig. 142. Fig. 143. Fig. 144. 
Figs. 142-144. Glassia obovata, Sowerby. 
Fig. 142. Interior ol' the peilicle-valve. 
Figs. 143,144. Views of the exterior. Natural size. (Davidson.) 
Brachial valve with an internal septum. The spiral cones have their bases 
toward the lateral margins of the shell and their apices at the center of the 
internal cavity; their position with reference to each other is therefore just 
the reverse of that in Meristella, Retzia, etc. The cones are laterally com¬ 
pressed, and the ribbon makes but few volutions. The loop originates as 
in Atrypa, 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, Atrypa obovata, Sowerby. Wenlock and Ludlow formations. 
In this genus and Cyclospira the spirals are at the extreme of introversion, 
and the structure of the brachidium in its entirety is quite similar to that 
