Affinities of the New-England Chitons. 121 



2. Tlie Chiton ruber is LejJtochiton ruber of H. Adams, and 

 is probably CaUochiton puniceus^ Couth., of the same author. 

 It is the Tonicia rubra of Graj's ' Guide,' to which he adds as 

 synonyms, in P. Z. S., marmorea and fulminata', and it also 

 appears in Gray's ' Guide ' as Corephium ? rubrum. It has 

 not the characters of any one of these ^om;- genera, in which our 

 two best authors have placed it. It belongs to Gray's genus 

 Ischnochiton [= Leindopleurus^ H. Ad., not Risso), section f, 

 "mantle-scales minute, granular ;" but as the gill-rows are 

 short, instead of surrounding the foot as in the typical species, 

 it is necessary to establish a fresh genus, Trachydermon. 

 The insertion-plates are, as in Ischnochiton and Chcetopleura^ 

 regularly slit and sharp all round. ]Mr. Emerton first ob- 

 served a great peculiarity in the animal, that there is a can- 

 cellated space between the posterior gill and the caudal extre- 

 mity. Prof. Verrill observed that in different specimens there 

 were eitlier one, two, or three rows of holes on each side. The 

 caudal lobe is generally figured as an anal tube; but in T. rubrum 

 it is an imperforate muscle, working the posterior part of the 

 girdle. The fteces were distinctly seen to escape, sometimes 

 on one side, sometimes on the other, as it appeared to me from 

 a slit on each side. 



3. The Chiton albus is Leptochiton albus of H. Adams, = 

 sagrinatus, Couth. I twice captured a live specimen ; but each 

 time it eluded the aftersearch. I do not doubt that this is 

 also a Irachydermon, but cannot vouch for the peculiar cha- 

 racters above quoted. The genus belongs to cold and tempe- 

 rate seas. 



4. The British C. marginatus is also a Trachydermon, and 

 not a Leptochiton. It is the C. cinereus of Lowe, Forbes, and 

 Hanley, but not of many other writers. Of the unique 

 American shell so called I can say nothing. 



5. The C. marmoreus, common at Eastport and northwards 

 to Greenland, is Tonicia of H. Adams and Gray, simply be- 

 cause the girdle is smooth. The true southern Toniciai^ how- 

 ever, have pectinated insertion-plates and ambient gills, like 

 the typical Chitons ; while the northern species so called 

 have sharp plates and short gills. They difler, in fact, from 

 Trachydermon simply in the girdle being destitute of the mi- 

 nute scales- I distinguish the group as ToniceUa. 



6. The C. mendicarius does not appear in the lists, and is 

 probably unknown in Europe. Fortunately a very few speci- 

 mens were dredged in the ' Bluclight,' one of them smashed but 

 very lai'ge. It is known outside by the minute bristles on the 

 girdle; but within it presents the very abnormal characters 

 which had befoi'c been observed only in the minute British 



