Vol. XI] BERRY— FOSSIL CHITONS 453 



Remarks: The 18 small Mopalia valves listed in the table 

 above from the Pleistocene of Santa Monica are mostly in very 

 mediocre condition and cannot be referred with certainty to any 

 of the known species. The largest [934] has the following 

 caliper measurements: long. 3.2; diam. 8.5; alt. 3.1 mm. Per- 

 haps it is possible that the specimens represent juvenals of 

 the foregoing species (ciliata) or even of muscosa, but further 

 material is needed to settle the question. Where the sculpture 

 is at all well preserved it is very sharp and beautiful. A single 

 specimen of undoubtedly the same species is here recorded 

 from the Pliocene of Rustic Canyon, Santa Monica. The 

 Pliocene age of this specimen is therefore desirable of con- 

 firmation. 



15. Mopalia, sp. indet. 



A single badly worn intermediate valve of what seems to be 

 an indeterminate Mopalia [954] is before me from Mr. Chace's 

 collections at Crawfish George's (Lower San Pedro Pleisto- 

 cene), San Pedro, California. 



Genus Placiphorella Carpenter, 1879 



16. Placiphorella velata Carpenter, 1879 



(Plate III, figs. 13-15.) 



1879. Placiphorella velata Carpenter in Dall, Proc. U. S. Nat. 



Mus., v. 1, pp. 298, 303, 307, pi. 4, f. 36-36a 



(radula). 

 1893. Placiphorella velata Pilsbry, Man. Conch., (1), v. 14, 



p. 306, pi. 66, f. 6-12. 

 1919. Placiphorella velata Chace and Chace, Lorquinia, v. 2, 



p. 43 [3] (recorded from Pleistocene of Pt. Fer- 



min, Cal.). 



Diagnosis 12 : Valves heavy, the median ones not beaked; 

 straight or even distinctly concave behind, extremely short and 

 wide ; practically unsculptured except for the lines of growth ; 

 lateral areas distinct and well raised, separated into low ribs 

 by a shallow central sulcus; tegmental border slightly false 

 beaked in front ; teeth of head valve short, numerous, primarily 



13 Description drawn in part from recent specimens. 



