492 PROCEEDINGS OF THE ACADEMY OF [AllSi., 



to be so greatly amplified to admit of the reception of the forms 

 now before us that the erection of a new group would seem to be 

 at present the safest course. 



Literature. 



Keep, Josiah. ('04.) West American Shells. San Francisco, 1904. 

 Pilsbry, Henry A. ('92.) Monograph of the Polyplacophora. Man. Conch. 



(1), XIV, 1892. 

 ('98.) Chitons collected by Dr. Harold Heath at Pacific Grove, near 



Monterey, Cal. Proc. Acad. Nat. Sri. Phila., 1898, pp. 287-290. 

 Thiele, Johann. ('10.) Revision des Systems der Chitonen. II. Teil. 



Zoologicn, Heft 56, Bd. 22, pp. 71-120, Pis. VII-X, 1910. 



Explanation of Plate XL. 



Fig. 1. — Mopalia heathii Pilsbry. Head valve, exterior. 

 Fig. 2.- " " " ' Third valve, exterior. 



Fig. 3.— " " " Tail valve, exterior. 



Fig. 4. — Mopalia thamnopora Berry. Head valve, exterior. 

 Fig. 5.— " " " Tail valve, exterior. 



Fig. 6.— " " •• Fifth valve, exterior. 



Fig. 7. — Mopalia heathii Pils. Sutural bristle. 

 Fig. 8. — Mopalia thamnopora Berry. Sutural bristle. 



