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tochiton. It is the C. cinereus of Loven, Forbes and Hanley; but, not 

 of many other writers. Of the unique American shell, so called, I 

 can say nothing. 



5. The C. mormoreus, common at Eastport and northwards to 

 Greenland, is Tonicia of H. Adams and Gray, simply because the 

 girdle is smooth. The true southern Tonicice, however, have pecti- 

 nated insertion-plates and ambient gills, like the typical Chitons ; while 

 the northern species, so called, have sharp plates and short gills. 

 They differ in fact from Trachydermon simply in the girdle being des- 

 titute of the minute scales. I distinguish the group as Tonicclla. 



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

 unknown in Europe. Fortunately a very few specimens were dredged 

 by the "Bluelight," one of them smashed, but very large. It is known 

 outside by the minute bristles on the girdle; but within it presents 

 the very abnormal characters which had before been observed only in 

 the minute British C. Hanleyi. This appeared as Leptochiton Hanleyi 

 in Gray's first paper, but as Acanthopleura Hanleyi in his " Guide," p. 

 183. But in the same book, p. 180, the same species reappears as 

 Hanleya debilis ; the genus (constituted for that species alone) being 

 said to have lateral tufts of spines; insertion plates entire, of ter- 

 minal valves alike. H. Adams, following this diagnosis externally, 

 described other species which really had these spine-tufts, though not 

 the internal characters. However, on examining every specimen of 

 the species in the market, I could not discern a single spine-tuft, 

 though announced by the accurate Loven. I found, however, excel- 

 lent internal characters. All the valves were destitute of insertion 

 plates, except the anterior one, which really was entire, having one 

 continuous plate, not slit. I did not know whether to believe my 

 own eyes, or the testimony of Loven and Gray, till Prof. Verrill 

 allowed me to open the large smashed specimen of C. mendicarius. 

 It proved to be a true Hanleia, according to my diagnosis, but not 

 according to Loven and Gray. I presume that the contraction of the 

 skin, in so minute a shell, led to the appearance of tufts, and that 

 Dr. Gray supposed that the posterior valve had an entire plate like 

 the anterior. I should be glad of the opinion of others', whether 

 the genus Hanleia should follow the type against the diagnosis, as 

 here given; or an unreal diagnosis against the type, as followed (in 

 part only) by H. Adams. The animal of this species resembles 

 Leptochiton in having short posterior gills, and a central anal tube 

 from which the fasces were seen to exude. 



7. A similar confusion attends the last and most remarkable species, 

 C. Emersonii. Several live specimens were dredged by the Bluelight. 

 one of extraordinary size ; and still more have been dredged by PI. 

 Dawson at Murray Bay. For the original species, C. vestitus, from 



