ORDOVICIAN FAUNAS. . 15 
St 
DALMANELLA TESTUDINARIA (Dal.). 
Platemxewhiess 1: 
1895. Orthis (Dalmanella) testudinaria W. & S., Pal. Minn., pt. 1, 
p. 441, pl. 33, figs. 17-22. 
Description. Adult shells subcircular and the younger ones irans- 
versely subelliptical in outline; hinge-line less than the greatest 
width; cardinal angles rounded, lateral and anterior margins broadly 
rounded, though the extreme front of the shell is sometimes straight 
for a short distance. Surface of both valves marked by unequal, 
angular, radiating coste, about ten or twelve of the largest. ones 
having their origin at the beak, the remainder being lateral branches 
from these. In some of the larger individuals as many as sixty or 
more coste are present along the margin of the shell. The branches 
from the main coste are small at first, but increase in size towards. 
the margin of the shell, and themselves give off additional branches. 
In many individuals this manner of branching gives to the coste a 
more or less fasciculate appearance, each fascicle having one large 
rib in the centre, with smaller ones on either side. In those specimens 
having the shell well preserved the bottoms of the grooves between 
the coste exhibit a series of fine, transverse crenulations. Pedicle 
valve convex, subcarinate along the median line, the lateral slopes 
nearly straight, the greatest convexity of the valve about one-third 
the distance from the beak. Cardinal area moderately concave, form- 
ing an angle of about 45° with the plane of the valve, about five or 
six times as wide as high. Delthyrium a little higher than wide. 
Brachial valve nearly flat, with a sinus beginning close to the beak 
and expanding in a broad, shallow depression towards the front. 
The dimensions of an average-sized specimen are: length, 8.mm.; 
width, 8.25 mm.; convexity of pedicle valve, 2.5 mm. 
Remarks.—This species is nearly as abundant in the Trenton lime- 
stone as Plectambonites sericeus. The New Jersey specimens are all 
of one variety, which are particularly characterized by the subcarinate 
pedicle valve and the rather coarse, fasciculately-arranged radiating 
coste. 
