CLASS III 



AMPHINEURA 513 



Two subdivisions of this family are recognised, according as the anterior and side 

 slits correspond in position with ribs on the external surface or not. Among the 

 genera included under the first section {Gallistoflacinae) may be mentioned the follow- 

 ing : — Gallistochiton, Nuttcdina, and Callistoplax Carpenter ; Grasfcdochiton Shuttle- 

 worth ; and Ceratozona Dall. Eepresentatives of the second subfamily {Ischnochitoninae) 

 are as follows : — Schizoplax Dall ; Tonicella, Trachydermon, and Dinoplax Carpenter ; 

 Gallochiton and Ischnochiton Gray ; Ghaetopleura Shuttleworth. 



Family 2. Mopaliidae Pilsbry. 



Valves externally divided typically into central and lateral areas, the posterior valve 

 with a sinus behind, one or two slits on each side of it or none ; intermediate valves each 

 with a single slit ; teeth smooth, sharp, often ivith thickened edges on the outside ; girdle 

 more or less hairy. Pleistocene and Recent. 



This family comprises the following genera : — Mopalia and Plaxiphora Gray ; 

 Placiphorella Carpenter ; and Placophoropsis Pilsbry. 



Family 3. Acanthochitidae Pilsbry. 



Valves more or less immersed in the smooth or hairy girdle, the tegmentum therefore 

 much smaller than the articulamentum ; the exposed stirface divided into a narrow dorsal 

 and wide latero-pleural areas, the latter formed by the union of the lateral and pleural 

 areas of typical Ghiton^. Insertion teeth sharp, rarely smooth; posterior valve either 

 slit like the head-valve, or having a. posterior sinus ; head-valve usually with five slits, 

 intermediate valves singly slit. Body never vermiform. Pliocene to Recent. 



The following representatives are to be cited : — Acanthochites Risso ; Spongiochiton 

 Carpenter ; Katharina and Amicula Gray ; Gryptochiton Midd. and Gray. 



Family 4. Cryptoplacidae Dall. 



Elongated or vermiform Ghitons loith small valves; insertion and sutural plates 

 strongly drawn forward, sharp and smooth ; the anterior valve ivith three to Jive slits, the 

 others with one slit on each side, or none; tail-valve having the miicro far posterior, 

 insertion plate continuous behind ; girdle very thick and wide. 



This is a highly specialised branch of a low group of Chitons, unknown in the 

 foasil state. Gryptoplax Blainville {Ghitonellus Lam.), and Ghoneplax Carpenter, are 

 examples. 



Suborder C. TELEOPLACOPHORA Pilsbry. 



All valves, or the first seven, with insertion plates cut into teeth by slits; the teeth 

 sharply sculptured {pectinated) outside by fine vertical grooves. 



Family 1. Chitonidae Pilsbry. 

 Gharacters those of the suborder. Tertiary and Recent. 



The family is illustrated ])y the following genera, of which only the first two occur in 

 the fossil condition : — Ghiton Linne ; Trachyodon Dall ; Eudoxochiton Shuttleworth ; 

 Tonicia, Schizochiton, Enoplochiton and Onithochiton Gray ; Acanthoplcura Guilding ; 

 Lorica Adams ; Loricella and -Liolophura Pilsbry. 



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