150 CHITON. 



Lepidopleurus (in part) Risso, Hist. Nat. Eur. Merid., p. 267. 



Oymnoplax GRAY, in The London Medical Repository, Monthly 

 Journal and Review, xv, p. 234 (Jan .-June, 1821.) 



Valves wholly external, the beak of the tail valve median or 

 anterior ; insertion-plates longer than the eaves, slit into teeth which 

 are deeply and finely pectinated, and typically project outward on 

 all the valves. Girdle covered with closely imbricating, convex, 

 smooth or striated scales. Gills extending the entire length of the 

 foot. 



History of names for Chiton. In the tenth edition of his Systema 

 Natures, Linne includes in the genus Chiton the following species : 

 hispidus, (" C. testa sexvalvi striata. Habitat . . "), tuberculatus t 

 aculeatus and punctatus. Of these the first, hispidus, is now univer- 

 sally admitted to be unidentifiable, as no information or reference 

 further than that quoted above is given. The next species is a well- 

 known West Indian form, and has been cited as the first species or 

 type of the genus by Spengler, Guilding, Gray, and nearly all 

 authors. Linne's third species, aculeatus, is apparently unidentifi- 

 able, but probably belongs to the genus Acanthopleura ; the fourth, 

 punctatus, is if possible less recognizable ; and even its modern genus 

 cannot be determined. The name Lophyrus Poli has been used for 

 the group by Messrs. Adams, but it can have no standing on account 

 of the fact that Poli proposed that name for the soft parts only, 

 retaining the name Chiton for the shells, in accordance with his 

 curious system of double naming. Poli's first species of Lophyrus is 

 L. melphictensis, which is the soft part of Chiton cinereus L. ! Only 

 one of Poli's four species belongs to the restricted genus Chiton. 

 The history of the name Lepidopleurus is given on page 2 of this 

 volume. The history of the name Gymnoplax is as follows : 



Gray, in his article " A Natural Arrangement of the Mollusca 

 according to their internal Structure" (Med. Repos.), under the 

 head of " Ord. 10 Polyplacophora," enumerates the synonyms of that 

 term, defines the order, and offers the following arrangement : 

 " a. Plates placed on the back of the mantle. 



1. Gymnoplax or gymnoplacidse. Acanthochitona. Chiton 

 facicularis. Leptochitona. Chiton marginatus. 



b. Plates sunken in the back of mantle. 



2. Cryptoplax. Chiton larvceformis." 



The inference from this would he that Gray intended to include 

 in "Gymnoplax or gymnoplacidse" all Chitons having exposed 



