Xvi POLYPLACOPHORA. 



The same is true of REEVE, who in 1847, published a monograph 

 containing 189 species in the Conchologia Iconica. The figures 

 of Sowerby and Reeve are generally good ; but they ignore inter- 

 nal characters, and their descriptions are totally inadequate. J. E. 

 GRAY, in 1847, (Ann. Mag. Nat. Hist, July-August, and P. Z. S.), 

 proposed a system of classification of Chitonidce, embracing many 

 new genera, but largely based upon Blainville's article of 1825. 

 Gray's system is as follows : 



I. Mantle simple, without any pores or tufts of spines on the sides. 



A. The plate of insertion of the anterior and posterior valves divided 

 into several lobes, and of the central valves into two lobes. 



a. Containing Chiton, Tonicia, Acanthopleura, Schizochiton. 



b. Containing Corephium, Plaxiphora, Onithochiton, Enoplo- 

 chiton. 



[c. Radsia, Callochiton, Ischnochiton, Leptochiton, subsequently 

 added by Gray.] 



B. The plate of insertion of all the valves with only a single notch on 

 each side. The valves more or less covered ; the hinder valve 

 with expanded plates of insertion (as in the central valves), with 

 only a single notch on each side, and a concave sinuosity below. 



a. Contains Mopalia, Katharina, Cryptochiton. 



II. Mantle with a series of pores (each furnished with a tuft of spines) 

 on each side. The plates of insertion of all the valves with only a sin- 

 gle notch on each side which is sometimes rudimentary. 



a. Contains Cryptoconchus, Amicula, Acanthochites, Chiton- 



ellus. 



Some inconsiderable transpositions and additions were made by 

 Gray in his Guide, 1857. This classification is accepted by H. & 

 A. Adams, in their Genera of Recent Mollusca, 1858 ; the two pri- 

 mary divisions being regarded as subfamilies ( Chitonince and Crypto- 

 placince) by them. The species of their lists in very many cases do 

 not belong to the genera to which they are assigned, the lists having 

 been compiled without regard to the characters of the insertion 

 plates. The main defects of this system are the greatly exaggerated 

 importance given to the development of girdle-pores, and the imper- 

 fect apprehension of the features of the insertion plates. Some 

 years before the date of Gray's last paper, J. R. SHUTTLEWORTH, 

 an Englishman by birth, but resident in Switzerland, studied the 

 Chitons carefully in the light of Gray's earlier paper, and published 

 a well-digested synopsis of the group (Bern. Mittheil, 1853), making 

 a number of decided improvements in classification. 



