AMPHINEURA 489 



Family 3. ACANTHOCHITIDAE. 



Shell reduced and more or less covered by the smooth or hairy (never 

 scaly) girdle: 6 genera. 



Key to the genera of Acanthochitidae here described: 



Oi Shell not completely covered. 

 6i Tegmenta bottle-shaped; last valve with a median sinus.... 1. Katharina 

 6, Tegmenta heart-shaped ; last valve rounded 2. Amicula 



Ca Shell completely covered 3. Cryptochiton 



1. Katharina Gray. Valves two-thirds covered by the girdle, the 

 exposed portion divided into dorsal and side areas ; insertion-plates sharp 

 and very long, that of the head valve with 7 to 8 irregularly placed slits ; 

 gills long and extending the whole length of the foot : 1 species. 



K. tunicata (Wood). Shell dark brown; girdle black, shining and 

 leathery; length up to 75 mm.; breadth 40 mm.: Alaska to Catalina 

 Island, from low- water line to 20 fathoms; eaten by the Indians. 



2. Amicula Gray. Shell with the valves externally scarcely visible, 

 the exposed part being heart-shaped and as broad as long; hinder valve 

 with a median sinus and a slit on each side : 3 species. 



A. vestita (Sowerby) {A. emersoni Couthouy) (Fig. 

 752). Length 50 mm.; breadth 35 mm.; color of shell light 

 drab; girdle brown, thin, and smooth, showing the valves 

 through it; adults with scattered tufts of hair: New Eng- 

 land coast north of Cape Cod in 5 to 30 fathoms. TmicuU 



3. Cryptochiton Middendorff. Valves concealed by (cfouid) 

 the leatheiy girdle and lacking tegmenta, their hinder 



margins produced backwards in a deep lobe on each side, the lobes fusing 

 across the median line: 1 species. 



C. stelleri (Midd.). Body oblong, brick red in color; covered with 

 minute spines; length 20 cm.: Pacific coast, south to Monterey, Califor- 

 nia, just below low tide ; eaten by the Indians. 



Suborder 3. TELEOPLACOPHORA. 



Shell of large size; the anterior valve similar to the posterior, and 

 similarly articulated; insertion plates on all the valves, finely pectinated 

 or grooved, blunt-edged and slit, the teeth all projecting outwards: 10 

 genera and about 80 species, principally in the Pacific. 



Chiton L. Girdle covered with imbricating scales; no eyes present; 

 gills extending the entire length of the foot: 36 species, principally in 

 the West Indies and the Pacific. 



C. tuberculatus L. Shell green or olive brown in color, generally 

 spotted; lateral areas with 5 radiating ridges; central areas with longi- 



