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



Measurements: Maximum length of largest specimen 

 [471a], 9.5; maximum width, 5.9; altitude, 1.4; length of 

 shell only (est.), 8.5; width of tegmentum of valve iv., 

 3.9 mm. 



Type: A shell preserved dry [S. S. B. 466], entered as 

 Cat. No. 3913 of the author's collection. Paratypes have 

 been deposited in the collections of the California Academy 

 of Sciences, the Academy of Natural Sciences of Philadelphia, 

 the United States National Museum, and the private collec- 

 tion of Mr. Allyn G. Smith. 



Type Locality : Under stones at low tide. White's Point, 

 Los Angeles County, California; Allyn G. Smith, August 

 14-18, 1916; 70 specimens. 



Remarks: It is a surprise to find a littoral species of such 

 abundance apparently undescribed, yet after the most ex- 

 haustive comparisons possible to me, I have been unable to 

 identify this very neat little species with any of the described 

 forms. I have been at particular pains in this connection to 

 re-examine the descriptions of the numerous Ischnochitons 

 described by Carpenter from Central and Southern California, 

 more especially since several of these still lack authentic 

 rediscovery and are but very insufificiently known. Without 

 access to the original specimens this naturally becomes a 

 hazardous task, but nevertheless I feel reasonably safe in the 

 conclusion reached. 



The descriptions of /. scahrico status remind one very much 

 of the present species, but fortunately I have seen authentic 

 specimens of this, and the comparison shows that it differs 

 distinctly in its conspicuously greater elevation, more numer- 

 ous ribs (3-5) of the lateral areas, and also (24-30) of the 

 anterior valve, and the fact that the lateral areas are only 

 slightly raised. The two species resemble one another in 

 the short, wide, dorsal girdle scales, more polished and per- 

 haps somewhat smaller in scabricostatus, and in the scaly- 

 granular character of the surface of the shell. 



/. retiporosus of northern waters impresses one as perhaps 

 being somewhat near of kin, but still no special comparison 

 is necessary to distinguish them. 



Minus a good lens, /. asthenes might at first glance be 

 confounded with the young of Callisto chiton decoratus punc- 



