472 



CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Ser. 



Recorded Range: 



Pleistocene: Upper San Pedro Series, Long Wharf 

 Canyon, Santa Monica, California (?!); Spanish Bight, San 

 Diego, California (!). 



Living: Monterey, California ( !), to Todos Santos Bay. 

 Lower California ( !). 



Material Examined: 



-3 



Valve 



Locality 



Collector 



Where Deposited 



§ 3'S 



Formation 



Period 



Int. 

 Inf. 



Long Wharf Canyon, Santa 

 Monica, Cal 



Long Wharf Canyon, Santa 

 Monica, Cal 



Spanish Bight, San Diego, 

 Cal 



F.C.Clark 



F. C. Clark 



Mrs. Kate Stephens . 



F. C. Clark Coll 



Berry Coll, Cat. 3979. 

 Berry Coll. Cat. 3925. 



[ 508] 

 [ 508] 

 [507] 



Upper San Pedro. 

 Upper San Pedro . 

 Upper San Pedro. 



Pleistocene 

 Pleistocene 

 Pleistocene 



Remarks: I. pectinnlatus is a characteristic representative 

 of a numerous and difficult group of Ischnochitonidce, which, 

 according to our present information, attains by far its most 

 remarkable development on the northwest coast of America. 

 Among this melange of species, but few of which have as yet 

 been discovered in the fossil state, /. pectinulatus is recognizable 

 chiefly by minor details of sculpturing, notably the divarication 

 of the lateral and terminal areas into distinct, strongly irregu- 

 larly multi-granose riblets (generally 5-6 in number on the 

 lateral areas), while a series of especially strong backwardly 

 directed tubercles (12-18 on a side) dentates the posterior 

 margin of all the valves but the last. There are 15-19 longi- 

 tudinal riblets on each side of the central region, overlying a 

 transverse grating rather stronger than usual. The riblets 

 of the jugal region diverge strongly on the second valve, but 

 only weakly or not at all on the succeeding valves, very unlike 

 the condition seen in the related cooperi and mertensii. 



The above notes, as well as the identification of the fossil 

 specimens, are based upon recent specimens from the San Diego 

 region. 



