PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 285 

 H. Cryptoidea. 

 With double sutural laminae. 



45. Cryptoeonchus Blaiuville. I 47. Cryptochiton Gray and Middendorf. 



46. Amicula Gray. 



a. Amicula s. s. Dall. 



b. Chlamydochiton Dall. I 



I. Chitonelloidea. 

 Tail plate fimuel-shaped. Laminae thrown forward. 



48. CMtonellus Blaiuville. [ 49. Clwneplax Cpr. 



a. Cryptoplax Gray. ( a. Chitotiiscus Cpr. 



It is hardly necessary to observe that the names here ascribed to 

 Gray, Shuttleworth, and other older writers are more or less restricted 

 so as to make them natural assemblages, which most of them orig- 

 inally were not. The subdivisions under similar names to be found in 

 Adams' Genera of Eecent Mollusca and Ch6nu's Manual are nearly all 

 heterogeneous assemblages. Some names which were found to have 

 been preoccupied in other groups have been replaced by new ones. 

 Nearly all the names enumerated have been made public, some of them 

 many years ago, others by Dr. Carpenter in his " Table of Kegular Chi- 

 tons," distributed in November, 1873, but of which a large proportion 

 of the copies printed are still on hand. Some appeared in different 

 papers on mollusca of the northwest coast of North America, published 

 by Dr. Carpenter from 1863 to 1874, and several were elucidated in a 

 paper on the New England chitons in the Bulletin of the Essex Institute 

 in 1873. A majority of them were also characterized by me (partly 

 from Dr. Carpenter's manuscript) in my Report on the Limpets and 

 Chitons of Alaska, &c., Proc. U. S. National Museum, December, 1878. 

 Such as still remained unpublished are now included in the following 

 analytical tables with additional notes elucidating their characters more 

 fully. 



It is believed that the publication of these tables will be beneficial in 

 several ways, as in giving a general view of Dr. Carpenter's classification, 

 and especially in calling attention to the characters which it is desirable 

 should be distinctly noted by those who may describe new species of 

 Ghitonidce, and for the want of which it is impracticable, in the majority 

 of cases, to properly classify or even to subsequently recognize the 

 species. The technical terms used and the relations of the several 

 parts have been explained in my report above mentioned, and it is not 

 considered necessary here to repeat the explanations. 



The publication of the entire monograph only awaits the preparation 

 of the illustrations, which has been delayed by circumstances entirely 

 beyond the writer's control. 



It may be thought by some who have not investigated the subject 

 that the group has been unduly divided. In regard to the permanent 



