276 
Tlie American Geologist 
Modiolopsis oviformis, n. sp. 
May, 1890 
Fig. 4. Modiolopsis oviforrnis, n. sp. Middle Trenton, near Burgin, 
Ky. a, perfect cast of the interior of a left valve of this species, b and 
c, anterior end and cardinal views of a free cast of the interior, nar- 
rower than usnal. 
Shell of medium size, regularly oval transversely, the pos- 
terior half a little the widest, with the greatest hight and 
length, averaging respectively as three or three and one-half 
is to five. Valves moderately and nearly evenly convex, with 
point of greatest convexity a little in front and above the cen- 
ter. Cardinal margin strongly arcuate ; basal margin with 
nearl}' the same amount of convexity; anterior and posterior 
ends nicely rounded, but with the former much narrower than 
the latter. Occasionally the posterior margin is produced 
slightly beyond an even curve in the postero-basal region. 
Beaks small, nearly terminal ; umbonal ridge nearly obsolete. 
Shell rather thick, strongest in the umbonal region, its outer 
surface nearly smooth, exhibiting only a few faintly impressed 
fine concentric lines. 
Casts of the interior, in which condition the species is 
usuually found, are terminated anteriorly by the well marked 
pair of muscular scars. The umbonal ridge is more pro- 
nounced than on the outside of the shell being defined anter- 
iorly by a distinct depression. Good casts show a well de- 
fined impression of the characteristic Modiolopsis cardinal 
fold or tooth between the beaks and the anterior muscle scars. 
A cast of a shell of the average size is 45 mm. long, 30 mm. 
