158 Systematic Paleontology- — Middle Devonian 



about two-thirds its length ami the interiors of both valves have numerous 

 and closely arranged small pustules. 



The most distinctive specific character of this species is the large 

 number of radiating, thread-like striae which cover both the coarser striae 

 and the interspaces. It most closely resembles C. vicinus (Castelnau) 

 but differs from that species in the larger number of striae and especially 

 in the fine radiating ones. 



Length, 6-9 mm. ; width, 10-12 mm. 



Occurrence. — Eomney Formation, Hamilton Member. B. & 0. 

 R. E. cut at 21st Bridge. 



Collection. — Maryland Geological Survey. 



Chonetes rugosus Kindle 

 Plate XIII, Figs. 7-9 



Chonetes rugosus Kindle, 1912, Bull. U. S. Geol. Surv., No. 508, p. 72, pi. iv, 

 figs. 5-7. 



Description. — Shell medium size transverse in outline, slightly convex 

 on the ventral side. Surface marked by fine closely placed striae number- 

 ing about 100. All of the striae bifurcate before reaching the margin, 

 some of them repeatedly. Six to ten concentric undulations or corruga- 

 tions cross the striae. These are strongest in the median and anterior por- 

 tions of the shell and die out toward the anterior margin. The hinge-line 

 is mucronate, the extremities extending considerably beyond the sides of 

 the shell. A strong rib-like process or pseudo hinge-line arises from the 

 hinge-line about midway between the beak and the extremity of the 

 mucronate extension of the hinge-line. This curves veiy gently upward 

 from the hinge-line and extends to or beyond its extremities. A peculiar 

 nonstriated, ear-like process is subtended between the hinge-line proper 

 and the pseudo hinge-line. This, on the inner surface, is marked by a 

 series of closely spaced diagonal denticulations. Dorsal valve and internal 

 characters are unknown. 



The peculiar denticulated ear-like expansion posterior to the hinge- 

 line distinguishes this from any other Chonetes. A single specimen 

 doubtfully referred to this species shows two short outward directed spines 



