54 THE AMPHINEURA 



sharp and smooth. Genera Cryptoplax, Blainville ( = Chtionellus, Lam.). 

 Girdle without pores. C. larvaeformis, Blainville (Fig. 26). Eastern 

 Archipelago. Choneplax, Carpenter. Girdle, with hair bundles within 

 pores. C. strigatus, Sow. 



SUB-ORDER 3. TELEOPLACOPHORA, Pilsbry. 



All the valves, or at least the seven anterior, with insertion plates 

 cut into teeth by slits. 



FAMILY 6. CHITONIDAE, Guilding. Characters of the Sub-Order. 

 SOB-FAMILY 1. CHITONINAE. No extra-pigmental eyes ; insertion plates 

 with pectinations between the fissures. Genera Chiton, L. Squamous 

 girdle. Eudoxochiton, Shuttleworth. Shaggy girdle. Trachyodon, Dall. 

 Rcukia, Gray. SUB-FAMILY 2. TONICIINAE. Extra-piginentar shell eyes. 

 Genera Tonicia, Gray. Girdle smooth or shaggy (Fig. 23). T. elegans, 

 Frembly. Acanthopleura, Gould. Enoplochiton, Gray. Squamous girdle. 

 E. niger, Barnes. Onithochiton, Gray. Schizochiton, Gray. Spinous girdle ; 

 posterior valve notched. S. incisus, Sow. (Fig. 28, C). Lorica, Adams. 

 Loricella, Pilsbry. Liolophura, Pilsbry. 



ORDER 2. Aplacophora, von Jhering 



( = Solenogastres, Gegenbaur = Telobranchia, Keren and Danielssen 

 = Scolecomwpha, Lankester). 



Our knowledge of the Aplacophora begins with Loven, who in 

 1841 described the genus CJiaetoderma, and with Michael Sars, who 

 mentions Neomenia in 1868, under the name Soknopus, but without 

 description. Chaetoderma was for a long time believed to be a 

 Gephyrean worm ; and Neomenia was at first included among the 

 Opisthobranchiate Gastropoda in a new Order, Telobranchia, by 

 Koren and Danielssen. 



Von Jhering was the first to point out the affinities of these 

 two remarkable organisms with the Chitones, and to unite them in 

 the new phylum Amphineura (1876); but he classed this phylum 

 with the Vermes. Gegenbaur also classed the two genera CJiaeto- 

 derma and Neomenia as worms under the name Solenogastres. But 

 Hubrecht demonstrated the molluscan nature of the new genus Pro- 

 neomenia, and its relationship to the Chitones. Lankester supported 

 this view, and was followed by nearly all contemporary zoologists. 

 It is generally believed that the Aplacophora are degenerate forms 

 of Amphineura, derived from a chitonoid ancestor. 



Definition. The chief characteristics differentiating the Apla- 

 cophora from the Polyplacophora are the following : ( 1 ) they are 

 worm-like in shape ; (2) the body is completely invested by the 

 mantle ; (3) the mantle is devoid of a shell, but bears numerous 

 calcified spicula over its whole surface ; (4) the digestive tract is 

 straight. 



