34 
BULLETIN OF THE LABORATORIES 
elongate; not very gibbous ; anterior dorsal margin inclined from the 
beak to the anterior end of the evenly curved lower margin, with 
which it united by an acute angle ; posterior dorsal margin gently sinu- 
ous, four times as long as the anterior ; posterior margin somewhat 
obliquely truncate, more prominent below ; greatest height at the umbo, 
posterior part somewhat narrowed. Surface marked by irregular con- 
centric striae and, at least posteriorly, by a few indistinct radiating 
lines. Length, .33, height, .17. It is more probable that this species 
is new, but some hesitation is felt in separating it from a minute form 
of nearly the same outline, in view of the poverty of our material and 
the variability of the species. 
AllorisiTia szibcuneata, M. and H. 
(Plate IV, Fig. I.) 
I am by no means certain regarding the identification of the frag- 
ments which have been referred to this species. However, it is cer- 
tain that a shell of about the same size and having the same form about 
the umbo and the same coarse markings is found at Flint Ridge. The 
species, moreover, is widely distributed, occuring in Utah and New 
Mexico, as well as Indiana and others of the central states. The de- 
scription is as follows : Shell large, twice or more times as long as 
high, gibbous anteriorly, compressed posteriorly, where the valves gape 
somewhat ; basal margin nearly straight, curved rapidly near the ante- 
rior, more slowly at the posterior ends; dorsal margin convex posteri- 
orly, giving the posterior outlines a somewhat spatulate form ; front 
margin rather narrowly rounded; beaks projecting well beyond hinge 
line; surface marked by well defined concentric lines. Length, near-, 
ly four inches. 
Genus Clinopistha. 
Clifiopistha radiczta, Hall. 
(Plate III, Fig. II.) 
Our specimen was associated with the forms elsewhere referred to 
Edmondia aspenwallensis, and resembles them very nearly. The out- 
line differs perceptibly, however, and the faint and very rugular con- 
centric stri^ are quite unlike the folds which ornament the shell of 
