1889.J 
307 
[Foerste. 
VALVE. 
v, ventral; d, dorsal. 
LENGTH. 
WIDTH. 
RATIO OF 
LENGTH TO WIDTH. 
NUMBER OF 
STRIDE IN TWO MM. 
NUMBER OF 
PROMINENT STKI.33 IN 
TWO MM. 
V. 
15.3 
21.7 
.711 
8 
5 
d. 
18.0 
25.6 
.703 
5. 5-6. 5 
5 
V. 
12.0 
17.4 
.689 
6-7 
6 
V. 
15.3 
22.3 
.686 
5.5-7 
5 
V. 
16 6 
24.6 
.675 
5.5— 6.5 
5 
V. 
9.2 
13.7 
.671 
6.5—7 
5.5 
V. 
14.6 
21.5 
.669 
6.5—7 
5 
d. 
16.0 
23.7 
.649 
5.5 
5 
We have not seen any of the typical forms from the Clinton of 
New York, but judging from the published figures it is possible 
that the Clinton forms from Tennessee may prove to be the same. 
Orthis elegantula, Dalman. 
Of twenty-six specimens found in the collection from Hanover, 
Ind., thirteen ventral and seven dorsal valves do not exceed 6 mm. 
in length. They correspond to the Ohio forms described under Or- 
this elegantula , var. parva. Three specimens are 7.5 mm. long, 
two ventral valves are 9 mm. long and one dorsal valve reaches 9.6 
mm. in length. The larger individuals of this species seem com- 
paratively rare both in the Ohio and in the Indiana Clinton lime- 
stones. 
In the collection from Cumberland Gap, Tenn., specimens of the 
following description are found. Dorsal valve convex or moder- 
ately convex, not flat or concave in the specimens found. Two deep, 
strongly marked pits in these casts, making angles of eighty de- 
grees with one another locate the short brachial processes. A much 
more shallow impression between these, nearer the cardinal margin, 
locates the cardinal process. 
From this a median groove extends forward, at first well-marked, 
but vanishing at or beyond the middle of the shell ; this places 
