RHYNCHONELLID^ OF THE HAMILTON GROUP. 361 



Leiorliynelius kelloo^p (n. s.). 



PLATE LVI. 



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 strioB upon the upper 

 half, which are less distinct below ; and the entire surface is marked 

 by fine thread-like concentric striaa, 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. 



[ Pai-eontology IV.] 46 



