62 THE NAUTILUS. 



EEMAEZS ON CEETAIN NEW ENGLAND CHITONS WITH DESCEIPTION 



OF A NEW VAEIETY. 



BY FRANCIS N. BALCH. 



The recent announcement by Ball ['05 a. and b.] of a new Chiton 

 from New England the first local addition to the group in many 

 years makes this a favorable moment to introduce an allied novelty 

 with a few remarks. 



Tonicetta Blaneyi Dall, was founded on a single specimen dredged 

 by Dwight Blaney, Esq., of Boston, off Ironbound Island, French- 

 man's Bay, Maine, in twenty fathoms. 



Its diagnostic marks consist substantially in conspicuously radially 

 ribbed lateral areas and terminal valves. 



Dall says it seems: " somewhat intermediate between Tonicella 

 and Trachydermon, with a leaning toward the former, while it 

 seems to be most nearly related specifically to Tonicella marmorea" 

 an opinion in which I concur. 



But this " intermediate " character raises the whole question of the 

 true relation of these forms, which I now propose to discuss. 



Trachydermon ruber and Tonicella marmorea are both common 

 north of Cape Cod in from five to one hundred fathoms; the former, 

 in my experience, outnumbering the latter (which favors the deeper 

 waters,) at least ten to one. 



They much resemble one another and in fact Gould ['70] (who 

 retained them both in the Linnean genus Chiton) says of ruber: " It 

 is not difficult to distinguish at sight well marked individuals of this 

 species from those of (7. fulminatus " (i. e., Tonicella marmorea.) 

 " But there are intermediate specimens which it is not easy to pro- 

 nounce upon. In general, this species is smaller, more solid, more 

 convex, the valves more beaked, lines of growth more deep, the zig- 

 zag lines never appearing, though the posterior margin of the valve 

 is sometimes dotted with white and red. The impunctured or un- 

 granulated surface, however, is the best, as it is a constant, charac- 

 teristic." 



But Gould's diagnostic points will not stand. The color-patterns 

 do duplicate, and the surface of ruber is punctate, as Dall has him- 

 self pointed out ['79]. I may add that in the coarseness of the punc- 

 tation the two overlap. 



The fact is, as Gould indicates, that while the extremes of the two 



