120 Mr. P. P. Carpenter on the Generic 



rated as CJiitonelhis. The consequence has been that very 

 little is known of most Chitonida except the external cha- 

 racters — the differentiation shown in the soft parts, and even 

 in the shelly valves, having been overlooked. 



We have been fortunate, during the explorations of the U. 

 S. Fish Commission, in observing four species alive ; another 

 was taken alive at Eastport last year ; a sixth has been cap- 

 tured on the southern coast. These are all as yet known to 

 inhabit the American Atlantic seas from Labrador to Florida. 

 A seventh, called Chiton cinereus^ is said to have been taken 

 alive by Dr. Pickering, and to be in the collection of the 

 Philadelphia Academy of Natural Sciences ; but it may prove 

 to belong to one of the other species, or to be a ballast specimen. 



The six authentic species present well-marked characters, 

 ranging under five genera. 



It may be premised that the Lamarckian genus Chiton was 

 first divided by the Rev. L. Guilding according to the ex- 

 ternal characters of the West-Indian species. About the same 

 time the Rev. T. Lowe published the peculiarities in the in- 

 sertion-plates of the British species. Both papers appeared 

 in the ^ Zoological Journal.' Dr. Gray, however, was the first 

 to present, in the ' Proc. Zool. Soc.,' a full description of the 

 fonns of Chitonidfe, accurately arranged under genera and 

 sections, partly according to the external, but principally 

 according to the internal characters. Mr. Heniy Adams, in 

 compiling the ' Genera ' from H. Cuming's collection, was 

 not allowed to examine the insertion-plates. He thought he 

 saw, however, a correlation between the internal and external 

 marks, and accordingly redescribed Gray's genera, with lists 

 of species, according to the sui'face-diagnosis. Gray, in his 

 ' Guide,' unfortunately copied from H. Adams's lists without 

 examination. Lastly, Chenu, as usual, reproduced the mis- 

 takes of H. Adams, with fresh ones of his own. 



Having had unusual opportunities of dissecting out the 

 valves of Chitons, I have felt compelled to rectify the pre- 

 viously published lists, and also to propose various new genera. 

 These I communicated to Mr. Binney while his edition of 

 Dr. Gould's ' Invertebrata ' was passing through the press ; but 

 he did not think well to alter the position of every one of our 

 species, as I feel compelled to do. 



1. The Chiton apiculatus does not appear in H. Adams or 

 Gray. It is a true ChcBtopleura, distinguished by the thin 

 hairy girdle, regular valves with sharp teeth, and long series 

 of gills. I have not seen it alive. It ranges from Southern 

 Massachusetts to Florida. The genus is for the most part 

 tropical. 



