BRAcHIOPODA. VT 
inclined backward, and uniting to form a stem which bears a 
short bifurcation at its extremity. 
The muscular area is elongate-ovate and more or less distinctly 
separated into anterior and posterior scars. Surface of the 
valves smooth or with fine concentric growth strie.  Shell- 
substance fibrous, impunctate. 
Type, Meristina Maria, Hall. Niagara group. 
Distribution. Silurian. 
Glassina, Hall. 1893. 
Shells small, biconvex, smooth. Spirals everted ; jugum form- 
ing neither athyroid saddle nor upright stem, but giving off at 
the junction of the lateral branches two linear processes; the 
whole apparatus having thus the form of an inclined x, with its 
upper tips curved outward. 
Type, Gtassina leviuscula, Sowerby (sp.). Wenlock limestone. 
But one species has been recognized. 
Merista, Suess. 1851. 
(Plate 33, figs. 8-15.) 
Synonym ; Camarium, Hall, 1859. 
Shells transverse or elongate, both valves generally inflated ; 
anterior margin sinuate, producing a fold and sinus on the mar- 
ginal portion of the brachial and pedicle-valves respectively. 
In the pedicle-valve the apex is perforated by a circular fora- 
men, which, however, is usually concealed at maturity, by the 
incurvature of the beak ; deltidial plates rarely retained. On the 
interior the teeth are prominent and are supported by dental 
plates which extend either for a short distance into the interior 
cavity or are considerably produced at their bases as thickened 
ridges. Between the dental plates is an arched free plate (the 
“ shoe-lifter” process) attached by its posterior and lateral mar- 
gins, but at its anterior margin extending beyond the dental 
lamellz and rising in a low, broad curve. In rare instances this 
process, from its origin, bears a sharp median carina which makes 
the anterior margin highly angulate. The muscular area appears 
to be limited to the space between the dental lamelle and to the 
surface of the “ shoe-lifter.” 
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