12 University of Michigan 
The pseudocardinals of the figure of the type of £. plexus 
distinctus (C. and F., 1894) resemble the juvenile form, but 
the description sounds more like those of the adult, in which 
the posterior pseudocardinal of the right valve is very heavy, 
jagged, and almost quadrate. 
VARIATION IN EF. plexus distinctus (C. and F.) 
E 
& 
= 
as 
0 
5 
Ho 
E. semigranosus 98 
E. plexus distinctus 79 
E. plexus crocodi- 
larum 90 
U. testudineus Mo. 91 
U. morini Mo. 75 
P. kuxensis 
Frierson 50 
Plate I, fig. 3 38.5 
Plate II, fig. 8 59.5 
fig. 16 62 
fig. 15 67 
fig. 17 690 
fig. 9 69.5 
fig. 14 75 
fig. 10 77-5 
fig. 13 80 
fig. II 82.5 
fig. 18 82 
fig. 12 84 
fig. 19 94 
Mean of 39 
specimens 75.0 
ao | Height-index 
w 
in per cent 
ie) 
70 (47.5) 
72(50.5) 
64(48) 
69(53.5) 
60(48) 
67(55) 
61 (490.5) 
61(51) 
61(57) 
64 
Extremes of lot 38to94 60to 72 
Diameter-index 
in per cent 
32 
42 
46 
37 
37 
34 
33 (12.5) 
39(23) 
40(25) 
42(28) 
36(25) 
37 (26.5) 
35 (26.5) 
44(33-5) 
35 (28) 
51 (42) 
43(35) 
50(42) 
42(30) 
4I 
33 to 48 
(type, C. and F., 1894) 
(type, /. c.) 
(Simpson, 1914; C. and F. 
same proportions, but 
smaller specimen) 
(C. and F., 1894) 
(C. and F., 1894) 
(Frierson, 1917) 
(Cf. kuxensis) 
(distinctus sculpture) 
(nearly smooth) 
(practically smooth) 
(plicate to pustulate) 
(Cf. testudineus) 
(distinctus sculpture) 
(sculptured dorsal) 
(peculiar, smooth shell) 
(all sculpture eroded) 
(compare morini; double 
posterior ridge) 
(Cf. crocodilarum; heavy) 
(largest spezimen) 
