ACANTHOCHITES. 7 



The Chitonellidce betray unquestionable proofs of descent from a 

 stock distinctly Acanthochitoid in its organization ; but their special 

 characters render it useful to treat that group as a separate, though 

 closely allied, family. 



See Vol. XIV, p. xxxii, paragraph bb for synopsis of genera. 



Subfamily ACANTHOCHITIN^E. 

 Genus SPONGIOCHITON Carpenter. 



See Vol. XIV, p. 26. This is probably a valid genus, allied to 

 Acanthochites but distinguished by the anterior dilation of the girdle 

 and the more regular slitting of the tail valve. 



Genus (?) LEPTOPLAX Carpenter. 



See Vol. XIV, page 25, where this genus was erroneously included 

 in the Ischnochitonince. Specimens should be critically examined 

 now that it is placed next to Acanthochites, for it may prove to be a 

 subgenus or section of the latter, near JVotoplax. 



Genus ACANTHOCHITES Risso, 1826. 



Acanthochites, Acanthochcetes and Acanthochiton of authors, + 

 Phakellopleura Guild, (haud Shuttlw. \),-}-Phacellopleura, Macan- 

 drellus and Stectoplax of Carpenter, -{-Notoplax Ad.,-{- Cryptoconchus 

 (Blainv.) Guild. 



Valves partially buried in or covered by the girdle, the exposed 

 part consisting of a smooth or striated dorsal band, and granulated 

 side-areas, the latter sometimes lacking. Anterior valve with 5 sym- 

 metrically placed slits ; median valves with 1 slit on each side ; pos- 

 terior valve with two or several slits. Girdle varying from densely 

 hairy to naked, but always having four bristle-bearing pores around 

 the head valve, and a single series of pores on each side placed at 

 the sutures. Gills short, extending forward from one-third to three- 

 fourths the length of the foot. 



This genus is distinguished from Leptoplax, Spongiochiton and 

 Katharina by the presence of bristle-bearing pores at the sutures, 

 and from the first two moreover by the less regular slitting of the 

 posterior valve. The genus Katharina differs from Acanthochites 

 further in the more numerous, unsymmetrical anterior slits, and in 

 the gill-row, which is as long as the foot. 



Acanthochites is the only genus (of more than one species) in which 



