PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 629 
specimen figured by Hall (Pal. New York, vol. 1, pl. 33, fig. 13c-d). Through 
the kindness of the American Museum of Natural History and Dr. N. D. Newell, 
the writer was permitted to examine this specimen. 
The type lot of R. increbescens consists of four specimens. Two of them, 
figures a,b and c,d, on plate 33, figure 13, are similar and probably were derived 
from the same bed. The third specimen, represented by figures e,f, is black in 
color, is wider and thicker, and is probably from a different part of the Trenton 
limestone. The last specimen is even larger than the third and has a strongly in- 
curved beak and considerably swollen brachial valve. It seems quite different 
from the others. 
The type specimen selected by Wang is small; length 11.1 mm., width 
12.2 mm., and thickness 8.2 mm. None of the original shell remains on this 
specimen, but Hall (Pal. New York, vol. 1, p. 147, 1847) implies that it was 
marked by “flexuous imbricating striae.”” The sulcus is marked by 3 costae, the 
fold by 4, and the flanks by 6 or 7. Unfortunately, the fact that the specimen is 
essentially a cast of the interior makes it impossible to determine any of the im- 
portant beak characters, but it does permit description of some of the interior 
details. The pedicle valve had a moderately deep delthyrial cavity defined by 
short, delicate dental plates. No trace of the musculature appears on the cast. 
The interior of the brachial valve was provided with a median septum reach- 
ing to about the middle and supporting a small cruralium. The hinge plate is 
divided with the halves somewhat concave but their shape not determinable. 
Muscle marks are not determinable. On the filling of the cruralium a short, thin 
white line indicates the presence of a small cardinal process. The latter feature 
does not appear on the second specimen which is similar to the lectotype. 
This type of interior is characteristic of several species of the middle part of 
the Trenton. Along with this interior goes an imbricate ornamentation and beak 
characters that set Rhynchotrema off from Wang’s genus Lepidocyclus. 
The generic characters of RAynchotrema are here defined as follows: triangu- 
lar, costate, rostrate shells usually with lamellose ornamentation; pedicle valve 
with delthyrium partially closed by narrow, elongate deltidial plates on the sides ; 
beak often resorbed by pedicle pressure to form a small, round foramen ; dental 
plates short ; teeth thick and stout, with large fossettes. 
Muscle field triangular with diductor scars enclosing the adductors; adduc- 
tor scar somewhat heart-shaped, large. Brachial interior with divided hinge 
plate ; sockets deep ; socket ridge narrow ; hinge plate gently concave, subtriangu- 
lar ; crura curved, moderately long; cardinal process slender to thick, often fill- 
ing the cruralium; median septum extending to the middle. 
RHYNCHOTREMA KENTUCKIENSE Fenton and Fenton 
Plate 130, A, figures 1-8 
Rhynchotrema kentuckiense FENTON and Fenton, Proc. Iowa Acad. Sci. for 1922, vol. 209, 
p. 67, pl. 1, figs. 4, 5; 18-22, 1924. 
