Lorraine Faunas of New York and Quebec 273 
of the shell, and, therefore, did not exhibit the longitudinally 
striated ligamental area. It is evident now that the flexure of 
the outer layer of the shell, along the hinge-line, has no connection 
with the method of attachment of the valves to each other. The 
so-called single prominent linear posterior tooth in each valve 
is the posterior crural ridge or posterior half of the jugum. 
13. Byssonychia radiata, Hall 
(Plate III, Figs. 12 A, B, C) 
Byssonychia radiata was described from the Lorraine of New 
York, and various specimens from the Cincinnatian of Ohio, 
Indiana, and Kentucky were identified with it. Among the Lor- 
raine localities are mentioned: Boonville and Turin, in Lewis 
county; at Lorraine, Jefferson county; at Pulaski, Washington- 
ville and Mexico, Oswego county; near Rome, in Oneida county; 
but Fig. 4a on plate 80, accompanying the original description, in 
the Paleontology of New York, vol. I, represents a specimen ob- 
tained at Pulaski, and this is regarded as the type, while the speci- 
men illustrated by Fig. 46, obtained from an unknown locality in 
the same county, is regarded as the cotype. 
Fig. 46 comes nearest to presenting the correct outline of the 
shell, especially those with the average number of plications. The 
upper part of the anterior margin is slightly concave owing to the 
forward curvature of the shell at the beak and the incurvature of 
the anterior face of the shell toward the byssal opening. The upper 
part of the umbonal ridge is never angular as in Byssonychia 
richmondensis. The angle between the anterior face and the cardi- 
dinal margin usually varies between 85 and almost 90 degrees, 
but occasionally is as low as 80 degrees. The length of the cardi- 
nal margin usually is about half the greatest length of the shell, 
from the beak toward the posterior part of the nearly evenly con- 
vex basal margin. Occasionally, the cardinal margin equals 
about three-fifths of the greatest length of the shell. The ratio of 
the greatest width to the greatest length, measured diagonally 
across the shell from the beak to the posterior part of the basal 
margin, usually is about 77 per cent, but may vary from as low as 
70 to as high as 81 per cent. The convexity of the single valve 
usually does not exceed 6 mm. in a shell having a maximum 
length of 36 mm. Shells exceeding 40 mm. in length are rare. 
