Vol. VII] BERRY— WEST AMERICAN CHITONS 247 



Considered in connection with the figures given by Pilsbry 

 ('93, pi. 15, figs. 34-37) and myself ( :11, pi. 40, figs. 1-3. 7), 

 the table appears to me conclusive that the specimens identified 

 by me in 1911 as Mopalia heathii (column 4 above) are cer- 

 tainly congeneric if not specifically identical with Trachyder- 

 mon fleet ens Carpenter, as interpreted by Pilsbry (column 2). 

 Down even to such details as size, color, and station the par- 

 allel is an instructive and telling one. But in view of the ad- 

 mitted source of possible error due to my having access to 

 neither of the type specimens concerned, it would be folly to 

 overlook the difficulties offered by the various discrepancies in 

 columns 1 and 3. As to column 1, the only trouble lies in the 

 large number of slits quoted for the head and tail valves and 

 the description of the girdle. The former may or may not be 

 an essential matter, depending on whether the number printed 

 be a lapsus (which I do not believe), or may indicate an ab- 

 normal specimen, or may (which appeals to me as the most 

 probable) come within the limits of normal variation, already 

 noted as considerable in the Monterey specimens described in 

 column 4. The discrepancy in the description of the girdle in 

 column 1 as compared with column 4 is also shared by column 

 2. This appears at first sight the most serious of all, but I think 

 is very easily accounted for by the very delicate and brittle con- 

 sistency of the bristles, which I find to be almost invariably 

 broken off in dried specimens in such a way as frequently not to 

 leave the slightest trace of their previous existence. This is 

 brought out very clearly in the series of specimens taken at 

 Forrester Island by Willett, all of which were preserved dry, 

 but which reached me soon enough afterward so that 1 was able 

 to make out the character of the bristles. In most of these the 

 bristles, however, appear either as mere stubs or so nearly in- 

 distinguishable that in the absence of some suspicion of their 

 presence they might never be detected. It is only in living or 

 alcoholic material that the full characters of this species are 

 evident." 



It IS worth while noting that specimens from the original lot of "Traclwdermon 

 tlectens moniereyensis Bartsch", a nowen niidnin which has appeared several "times in 

 print, are in every respect completely identical with the specimens referred to by me 

 as M. heathii in column 4 above. From similar evidence there is no doubt that "Chato- 

 pleura rosetta Bartsch", another nomen nudum which has found its way into the 

 literature, falls into the absolute synonymy of Dendrochiton thamnopora. I can as yet 

 discover no evident connection of this species with the genus Chatoplcura. 



