BRACHIOPODA. 367 
Tretnatis.l 
Genus TREMATIS, Sharpe. 
1847. Trematis, SiiABi'K. Quarterly Journal Geological Society, vol. iv, p. 66. 
1892. Trematis, Hall. Palaeontology of New York, vol. viii, pt. i, p. 138. 
Description: "Shell subcircular or transversely oval in outline. Pedicle valve 
unevenly convex, more or less depressed over the posterior region; apex at or behind 
the center; directly beneath it begins the pedicle-fissure, which transects the shell, 
vertically widening to the posterior margin with straight or outwardly-curving 
edges. Brachial valve evenly convex, with its apex marginal and slightly projecting. 
On the interior, the pedicle-valve shows a faint median furrow extending from the 
angle of the fissure to the apex of the shell; this groove widens at its apical termina- 
tion and may represent a point of muscular attachment. The sides of the fissure are 
often thickened by callosites similar to those sometimes seen in species of Orbkulo- 
idea. From the apex of the valve extend radiating and branching vascular sinuses. 
"In the brachial valve the posterior margin is much thickened and broadly 
grooved to allow the extension of the pedicle. This thickening does not take the 
form of a cardinal area or shelf, but is rather a callosity closely appressed against 
the interior surface of the shell, the central portion being projected beyond the 
margin of the pedicle-valve. Directly below and in front of this area are two 
transversely elongate scars, adjustors or posterior adductors, which are usually 
partly concealed by the progressive overgrowth of the cardinal thickening. A faint 
median septum begins between these scars and passes forward, becoming more 
prominent over the tongue-shaped median elevation which separates the large 
central scars. These impressions are oblique and are not simple, each appearing 
to be composed of two, if not three distinct scars, making a posterior, a median and 
an anterior pair. What appears to be the posterior pair is small, and sometimes 
quite sharply defined, the central pair very much larger, and the anterior pair 
narrow, situated at either side of the angle of the median callosity and separated 
by the apex. The specialization of the first of these scars is not satisfactorily estab- 
lished; the entire impression is deeply excavated. In some well preserved speci- 
mens there is also evidence of external marginal scars lying just in front of the 
outer end of the posterior adductors. 
"Surface of both valves more or less completely covered by a beautiful orna- 
mentation consisting of punctures or small pittings of varying depth, arranged 
either in quincunx (T. terminalis) or in radiating rows; in the latter case they may 
be distant from one another without intervening ridges {T. tanbonaf a), or lie in radi- 
ating furrows, when they are either circular {T. pnnctostriata) or subrectangnlar 
{T. ottawensis). 
