26 
BULLETIN OF THE LABORATORIES 
mis with which it is associated. Our specimens average less than one 
inch in extreme width. The area of the ventral valve is rather low 
and arched and striate parallel to the hinge line. 
SPIRIFER MARIONENSIS, Shum. 
A comparison of Spirifer marionensis and S. bihlicatus is rendered 
the more necessary because of their close resemblance and importance 
as marks of given horizons. The following notes are the result of a 
careful study of a large suite from all parts of the state. 
The ventral valve of S. marionensis is more evenly and strongly con- 
vex and toward the hinge is more uniformly gibbous, it also projects 
farther over the hinge, thus the beak of S. biplicatus seems more acute ; 
the hinge line is more elevated and strongly arched in S. marionensis, 
while in the other species its sides are approximately parallel until the 
vicinity of the beak is reached, the area is strongly striate perpendicu- 
larly in S. biplicatus, while in S. marionensis there is also an evident 
transverse system and a thick ridge below ; in both species there are 
long sharp spines upon the hinge angles which may exceed one-fourth 
the, width of the body of the shell; the plicae are not strongly dichoto- 
mous in S. marionensis except near the beak, while S. biplicatus tends 
to develop a pronounced dichotomy or grouping in the ribs ; the sinus 
is more distinct and narrov/er below in S. marionensis ; the cast in S. 
marionensis is pustulose about the umbonal region while the rostral 
cavity is more deeply excavated though the teeth seem less prominent; 
other minor differences are observed in the comparison of the speci- 
mens. 
The dorsal valves differ in proportions, S. marionensis being rather 
shorter and having in many cases a slight sinus instead of a fold or, at 
any rate, no prominent elevation tow'ard the front; the fold in S. biplica- 
tus is generally well-marked and often high and is further distinguished 
by the marked dichotomy of the plicse. 
Spirifer maidonensis marks a horizon some seventy feet below 
conglomerate I, and is known to extend along this line from Richland 
county to the Ohio river at Portsmouth and Sciotoville. Its absolute 
horizon is not seen in the northern part of the state, but some of the 
associated fossils seem to occur at the base of the exposure at Lodi 
with Sp. biplicatus and Entolium aviculatum. It is not improbable 
that S. biplicatus is a lineal descendant of the older form and it is 
