Vol. IX] BERRY— NOTES ON WEST AMERICAN CHITONS 3 



placed in my hands for study a few specimens of chitons from 

 the collection of the late Dr. J. G. Cooper, which are of inter- 

 est as having presumably been determined by Dr. P. P. Car- 

 penter. Among these I have been interested to find a single 

 specimen, represented by a few loose valves, of the very insuf- 

 ficiently known "Trachydermon gothiais" of Carpenter ('64, 

 p. 649; '66, p. 212). This bears the Catalogue Number 2388 

 [S. S. B. 478], and was taken by Dr. Cooper at San Pedro, 

 California, on shells of Haliotis. At near the same time a 

 second specimen came to me through the generosity of Mr. 

 W. H. Golisch of the Southwest Museum. This one, which 

 is fortunately complete, was found by Mrs. Golisch at Dead 

 Man's Island, San Pedro, California, in 1909 [S. S. B. 1060]. 

 For some time I have felt that gothiciis constituted a distinct 

 element of its own in the heterogeneous mixture comprised in 

 the Carpenterian genus Trachydermon, yet I was not alto- 

 gether prepared to find revealed a second species of my own 

 group Dcndrodnton (Berry :11, p. 487), of which D. tham- 

 noponis (Berry) stands as the type and, up till now, the only 

 known species. This group was founded largely because of 

 its girdle characters, and of course one would not expect the 

 complex and fragile setae to persist in dried specimens such 

 as these, but in the specimen found by Mrs. Golisch a few 

 pore-like dots are evident opposite the sutures in situations 

 corresponding to the position of the major series of setae in 

 D. fhamnoportts. From this circumstance, coupled with the 

 fact the shell characters of the two species are evidently but 

 elaborations of the satne general plan, I think there is no 

 question that the two are congeneric. On the other hand 

 their specific separation would appear to be easy. The more 

 conspicuous features in which D. gothiciis differs from thain- 

 noporus are : 



( 1 ) the greater elevation and more acute angle of the 

 ridge; 



(2) the much narrower, more numerous (about 13 on the 

 central valves), and straighter ribs of the pleural areas, blend- 

 ing into a rather obscure, fine, irregular, longitudinal thread- 

 ing on the jugal tract; 



(3) the relatively solid texture of the interspaces between 

 the pleural ribs ; in thamnoporus, under moderately high 



