DEVONIAN FAUNAS. 329 
in front. Hach valve marked by twenty to twenty-four simple, an- 
gular, radiating plications, three or four of which usually occupy the 
fold and sinus. 
The dimensions of a nearly-perfect individual are: length, 16 mm. ; 
width, 14 mm.; thickness, 9 mm. 
RENSSELAERIA SUBGLOBOSUS MN. Sp. 
Plate XLII., Figs. 11-18. 
Description.—Shell subglobular in form, longer than wide. Pedicle 
valve strongly-convex, its greatest elevation near the middle, some- 
times slightly subcarinate along the median line near the beak. Beak 
sharply-pointed, closely incurved over that of the opposite valve. 
Brachial valve a little less convex than the pedicle, its greatest ele- 
vation near the middle. Surface of each valve marked by from fifty 
to sixty simple, rounded plications, which become obsolete before 
reaching the beak. . 
The dimensions of an average specimen are: length, 18 mm.; width, 
16 mm.; thickness, 11.5 mm. 
Remarks.—This species is one of the very abundant ones in the 
“trilobite bed.” It resembles Rk. equiradiatus, but never attains the 
size of that species, the largest specimen observed out of several hun- 
dred examined, being 21 mm. in length, while adult indiyiduals of 
R. equiradiatus are 30 to 35 mm. in length. &. subglobose is also 
proportionally wider than R. equiradiatus. The species also re- 
sembles R. mutabilis, but grows larger than that shell, is smoother, 
not being so conspicuously marked by concentric wrinkles of growth, 
and bears a greater number of plications. 
SPIRIFER MURCHISONI Castel. 
Plate XLII., Fig. 26. 
See, also, p. 354, pl. NLVIITI. 
A few specimens of this Oriskany species have been observed. 
They do not differ essentially from those in the higher beds except 
in not reaching the maximum size of the later shells. 
