OF DENISON UNIVERSITY. 
63 
Myalincb ii%ichi£ciJiensis , Win ? 
(Cf. Af. swallovi. ) 
(Plate IV, Fig. 6.) 
The only difference between this species and M. swallovi of the 
coal-measures is in the greater size of the protuberance under the beak, 
but Meek says specifically: ^‘This species (M. swallovi) varies some- 
what in the size of the protuberance under the beaks; in some indi- 
viduals it is well developed, and gives the shell much the form of 
Modiola; while in others it is smaller, so as to present more the ap- 
pearance of a Mytilus.” Perhaps it may be sufificient to indicate the 
probable genetic relations of these forms. 
Modiola luaverliensis , sp. n. 
(Plate I, Fig. 9 ; Plate IV, Fig. ro; Plate VII, Fig. 29?) 
(There has been no opportunity to consult the description of M. 
metella, H. so the possibility of agreement with this Chemung fonrs 
is not excluded.) 
Nearly like M. nevadensis, WaL, but less elongate. Transverse- 
ly elongate, narrowly and uniformly rounded anteriorly, lower outline 
very gently curved, posterior end rather more broadly rounded than 
the anterior, the outline above diverging rather strongly to a point be- 
tween the middle and the posterior third, where it meets the nearly 
straight hinge. Beak posterior, somewhat overhanging. Post umbo- 
nal slope quite well marked near the convex urnbonal region, poste- 
rior part of shell rather flat. Length somewhat greater than twice the 
width. 
A number of casts have been found in the freestone of the mid- 
dle Waverly. Those specimens preserving the shell markings differ 
slightly from the cast first referred to and have fine concentric striae. 
These may indicate a distinct species, but probably the apparent dif- 
ferences correspond toihe different states of preservation. 
