RHYNCHONELLIDiE OF THE HAMILTON GROUP. 
361 
Leiorliynclius Kellogg! (n. s,). 
PLATE LYI. 
Shell ovate or suborbicular, more or less rotund, sinuate in the middle; 
length and breadth nearly equal in the younger shells, the width 
becoming greater in old shells; the middle of the front abruptly 
truncate. 
Ventral valve gibbous a little below the umbo, curving gently to the 
sides and becoming gradually flattened in the middle, and deeply 
sinuate in the lower part. Beak closely incurved over the umbo of the 
opposite valve, with apex acute. 
Dorsal valve regularly convex in the middle and upper part, curving to 
the sides : the broad flattened mesial fold usually becomes developed 
below the middle of the length. 
Surface marked by low rounded plications, of which there are four, five 
or six, and sometimes ten in the mesial sinus, and a corresponding num¬ 
ber on the mesial fold. There are six or seven plications on each side 
of the mesial fold; and both these and the central ones usually extend 
no more than half-way to the apex, and sometimes not so far.. When 
the shell is preserved, there are fine radiating striae upon the upper 
half, which are less distinct below; and the entire surface is marked 
by fine thread-like concentric striae, which, at intervals, are crowded 
into stronger wrinkles. 
The casts show a narrow ovate muscular area in the ventral valve, 
with a slender process filling the rostral cavity. In the dorsal valve there 
is a strong septum, with narrow muscular imprints on each side, reaching 
below the middle of the length. 
A large individual of this species has a length of seven-eighths of an 
inch with a width of one inch. A smaller specimen has a length and 
width of three-fourths of an inch. 
[ Paleontology IV.] 
48 
