Vol. XI] BERRY— FOSSIL CHITONS 427 



11. Valves normally proportioned Mopalia 



1 1 '. Valves excessively short and wide Placiphorella 



12. Valves with beaded sculpture; tegmentum strongly de- 



veloped behind the articulamentum ; median valves 

 distinctly narrowed at sides ; tail valve with short, 

 stubby teeth and posterior mucro Chsetopleura 



12'. Lateral and terminal areas having heavy radial ribs; the 

 insertion plates short and curving out into the slits, 



which correspond in position with the radial ribs 



Callistochiton 



12". Valves normal, with variously developed sculpture and 

 sharply cut. even teeth throughout Tschnochiton 



Description of Species 



Family Lepidopleuridae 

 Genus Leptochiton Gray, 1847 



1. Leptochiton clarki Berry, new species 

 (Plate I, fig. 10.) 



Diagnosis: Valves small, delicate, without insertion plates ; 

 sculpture weak, consisting of rows of small granules, coalescing 

 or overlapping to form weak longitudinal riblets on the central 

 areas and radial ones on the lateral areas ; sutural laminae very 

 low and wide, blending evenly into the shell margin. 



Type: An intermediate valve, entered as Cat. No. 3987 of 

 the writer's collection [S. S. B. 605]. 



Type Locality: Upper San Pedro Pleistocene of Long 

 Wharf Canyon, Santa Monica, California; collector. Dr. F. C. 

 Clark ; 1 median valve. 



Range: Unknown except type locality as given above. 



Description: Intermediate valve small, high-arched, sub- 

 angular on the ridge, the side slopes arcuate. Lateral areas 



a. *~~s. 



Fig. 1 



Fig. 1. Leptochiton clarki Berry, new species. Dorsal aspect of type 

 valve [605] ; camera outline. 



