RAYMOND: NEW FOSSILS. 469 
at right angles to the plane of union of the valves, so that it is 
hardly seen from above. The teeth are short, strongly divergent, 
and are supported by low, rounded, stout dental lamellae which 
are parallel throughout the greater part of their length, but di- 
verge at the front. Between them are the elongate, narrow scars 
of the pedicle, separated by a narrow groove. In front of these 
muscles, and entering the angle formed by the divergent arms 
of the anterior ends of the dental lamellae, are the faint scars of 
the diductors and adductors. The adductors are elongate, al- 
most linear, separated by a narrow groove. The outHnes of the 
diductors are vague, especially toward the front; the scars are 
elongate, and extend nearly halfway to the front of the shell. 
Measurements. — Length of brachial valve measured on internal 
cast from hinge-line to front 33 mm.; width at hinge 30 mm.; 
greatest width 44 mm. ; length of pedicle valve measured on mould 
of exterior 39 mm., which is somewhat less than the true length; 
thickness of internal cast 22 mm. There are 10 plications in 10 
mm. at the front, and 14 in the same width at the sides. 
Comparisons. — The short wide outline of this shell distinguishes 
it sharply from Rensselaeria ovoides, but there are several similar 
shells in the Lower Devonian of Maine. Rensselaeria mainensis 
WilKams is a short shell, but the brachial valve is as long as wide, 
and the plications are coarser than those of the present species. 
R. mainensis agrees with Prorensselaeria rather than with Re7is- 
selaeria in having a divided cardinal process, and although it has 
a more fully developed median septum in the brachial valve than 
does P. nylanderi, it is probably to be referred to the same genus 
as that species. The only other species of Rensselaeria previously 
described from the Chapman sandstone is Rensselaeria atlantica 
Clarke. That species differs very much in its outline from the 
one here described, since the adult is longer than wide, and the 
width at the hinge is so great as to give the shell a square-shoul- 
dered appearance. This shell is a typical Rensselaeria, with the 
hinge-plate perforated at maturity, strongly impressed muscle- 
scars, and a well-developed septum in the brachial valve. Clarke 
has pointed out that the young shells of this species are less elon- 
gate than the adults, and some of them have a fully divideil 
hinge-plate, so that the young is more fully comparable to P. 
nylanderi than is the adult. 
