305 
[Foerste. 
about eight or nine within a width of two millimeters ; at more or 
less regular intervals, varying usually from four to six or seven, 
certain of the striae are slightly broader, and decidedly more ele- 
vated and prominent. Concentric striae, where preserved, are al- 
ways less prominent than radiating striae and are closely set ; 
some disposed at irregular intervals, and more prominent, form 
“striae of growth.*’ 
The more prominent radiating striae are usually best marked 
near the anterior border of the shell ; when they occur at greater 
intervals than one in four, one of the intermediate striae is apt to 
be more or less conspicuously developed. In the preceding table 
both the number of the striae and the intervals at which the more 
prominent striae occur are measured along the anterior border. 
Measurements are in millimetres. 
Professor Whitfield called my attention to the fact that in the 
genus Strophomena it is not infrequent that dorsal valves differ 
more or less from the ventral valves in the character of their orna- 
menting striae. In our specimens it seems as if the same feature 
could be noticed. Thus the ventral valves of the Tennessee vari- 
ety as a rule show stronger prominent striae and fewer intercalated 
finer striae than the ventral valve, while the dorsal valve never has 
the stronger striae very prominent, but these striae are only a little 
broader, and the intercalated striae are almost always abundantly 
developed. In the table just given this fact does not become prom- 
inent since the slight variations in the character of the striae are 
not so much regarded, whereas this character becomes prominent 
chiefly through the median intercalated striation of the ventral valve 
becoming slightly more prominent than the remaining intercalated 
striae. 
Specimens occur in the Clinton group at Fauver’s Quarry and 
Soldier’s Home, O., which cannot be distinguished from S. corru- 
gata , var. pluri- striata, except in size. As to their relative length 
and breadth there is a certain amount of variation. The character 
of the striae is much as in certain forms of var. pluri- striata. They 
have the corrugations which are supposed to characterize that spe- 
cies, but in reality belong to almost any thin-shelled form. We 
consider them as the young of Strophomena patenta, since they do 
not retain this character beyond a certain size but merge impercep- 
tibly into the forms with double curvature placed under S. patenta. 
On PI. vm, Vol. ii, Bull. Denison Univ., Fig. 35 represents such 
PROCEEDINGS B. S. N. H. VOL. XXIV 20 DECEMBER, 1889. 
