Vol. XI] BERRY— FOSSIL CHITONS 44 J 



Bed". The two principal living species are very similar to each 

 other but are supposed to be quite distinctly separable geo- 

 graphically, N. calif omica occurring from the neighborhood of 

 Point Concepcion as far north, perhaps, as British Columbia, 

 while TV. Hnxa (Carpenter) is recorded from Southern and 

 Lower California. 



When first received the median valve figured was thought to 

 be referable to N. fluxa rather than to N . calif omica. Receipt of 

 better material has caused me to revise this opinion, but I must 

 admit that even with recent material I am not always confi- 

 dent that I am able to draw a proper dividing line between 

 these two species. The fluxa-\\kt outline of the specimen under 

 consideration, however, seems clearly due to the erosion of the 

 entire posterior portion of the valve. It has the following 

 caliper measurements: length 5.3, diameter 6.8, alt. 3.6 mm. 



The largest perfect specimen seen is an intermediate valve 

 from the Chiton Bed [1027], and measures: length 8.7, di- 

 ameter 9.0, alt. 3.2 mm. A worn and eroded median valve 

 from the same exposure [1404] is much larger, its length 12.0, 

 diameter 16.7, and alt. 5.8 mm. 



Family Mopaliidae 



Genus Mopalia Gray, 1847 



8. Mopalia muscosa (Gould, 1846) 



(Plate IV, figs. 1-9.) 



1846. Chiton muscosus Gould, Proc. Bost. Soc. Nat. Hist., v. 



2, p. 145. 



1847. Chiton ciliatus Reeve, Conch. Icon., v. 4, Chiton, sp. 



124, pi. 19, f. 124; detail pi., f. 124 (not of Sowerbv. 



1840). 

 1847. Chiton collei Reeve, id., sp. 136, pi. 21, f. 136. 

 1852. Chiton muscosus Gould. Moll. U. S. Expl. Exped., p. 



313, f. 436. 

 1862. Chiton muscosus Gould, Otia Conch., p. 6. 

 1893. Mopalia muscosa Pilsbry, Man. Conch., (1), v. 14, p. 



295, pi. 63, f. 46-56^ pi. 64, f. 74. 

 1903. Mopalia ciliata Arnold, Mem. Cal. Ac. Sci., v. 3, p. 28, 



42, 85, 343 (recorded from Pleistocene of San 



Pedro, Cal.). 



