456 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Ser. 



Material Examined: 



Remarks: The specimen previously reported by Chace from 

 the Pleistocene of Deadman Island is the one before me. It is 

 an anterior valve of this very peculiar and unmistakable species, 

 the first to be reported in the fossil state, and perfect except for 

 the loss of the tegmentum by delamination. The Arnold 

 collection has since proved to contain a large and finely pre- 

 served intermediate valve of the same species from the Pliocene 

 of this island. Mr. Chace seems to be reasonably positive 

 that his specimen came from the Pleistocene and not from 

 the Pliocene, though whether from the Upper or Lower San 

 Pedro Series he cannot now be certain. The Stanford speci- 

 men has quite a different appearance lithologically and is 

 plainly marked "Pliocene" on the accompanying label. The 

 measurements of this specimen by caliper are: long, 22.8, diam. 

 26.7, alt. 8.5 mm. Both specimens are figured herewith. 



Family ACANTHOCHITONIM: 



Genus Acanthochitona Gray, 1821 



18. Acanthochitona avicula (Carpenter, 1864) 



(Plate VI, fig. 9) 



1864. Acanthochites avicula Carpenter, Rep. Brit. Assoc. Adv. 



Sci., 1863, p. 612, 650. 

 1866. Acanthochites avicula Carpenter, Proc. Cal. Ac. Nat. 



Sci., v. 3, p. 211. 

 1893. Acanthochites avicula Carpenter, Man. Conch., (1), v. 



15, p. 24 (after Carpenter). 

 1893. Acanthochites avicula var. diegoensis Pilsbry, id., p. 25, 



pi. 12, f. 52-54. 



Diagnosis": Valves rather delicate, carinated, sharply beaked ; 

 pleural and terminal areas ornamented with a "snake-skin pat- 



13 Description drawn largely from recent specimens. 



