CHITONID. 345 
ONITHOCHITON, Gray. Insertion-plates regular, flat behind ; 
anterior valve with many slits, middle with one, posterior with 
none; teeth serrate; eaves deeply furrowed; sinus moderate, 
lobed; girdle with chaffy hairs. C. Lyelli7, Sowb. (Ixxxvi, 82). 
PLACIPHORA, Gray. Insertion-plates regular, ribbed behind ; 
anterior valve with many slits, middle with one, posterior with 
none; teeth slightly propped ; eaves small; sinus small; girdle 
hairy, with regular pore-tufts. C. Carmichaelis, Gray. 
FREMBLYA, H. Adams. Valves regular, ribbed behind; the 
middle with one, anterior with many, posterior with no slits; 
teeth excurved; eaves small; sinus broad, shallow; girdle hairy, 
with regular pore-tufts. Distinguished by its excurved teeth. 
C. Collei, H. Ad. 
EUPLACIPHORA, Shutt. Sinus wide, planate; girdle set with 
bristles, not fasciculated. 
GUILDINGIA, Cpr. Valves partly immersed; girdle emar- 
ginate behind. C. petholatus, Sowb. (1xxxvi, 89). 
G. Mopaloidea. 
Tail-valve with posterior sinus and one slit on each side. 
MOPALIA, Gray. Shell regular; laminz lengthened ; anterior 
valve with six or more slits, the others with a single slit; last 
valve sinuate behind; sinus narrow; mucro median, depressed ; 
sutures indented; girdle wide, bristly, sometimes fissured be- 
hind, sometimes projecting anteriorly. C. Blainvillei, Brod. 
(Ixxxvi, 90). 
PLACIPHORELLA, Cpr. The hairs or part of them issuing in 
fascziculi from sutural pores. C. velata, Cpr. 
KATHERINA, Gray. Armor small; girdle smooth, much ex- 
panded in the sutures ; laminz greatly projecting anteriorly, the 
posterior valve lobate ; sinus deep,spongy. Branchie encircling. 
Distr.—C. tunicatus, Wood (Ixxxvi, 91). W. Coast America, 
California to Alaska, Kamtchatka. 
ACANTHOCHITON, Leach. Insertion-plates thrown forward, 
laminated ; anterior valve with five slits, middle and posterior 
valves each one; teeth long, sharp, smooth; eaves small; gills 
median; sinus deep, broad, spongy; girdle hairy, with long, fas- 
ciculated spicule. CO. fascicularis, Auct. 
MACANDRELLUS, Cpr. Valves partly immersed; mucro Isch- 
noidal ; posterior lamina rugosely lobate ; lateral area depressed. 
C. plumens, Cpr. 
STECTOPLAX, Cpr. Valves two-thirds immersed. 
NoTopLAX, H, Adams. Tail-plate crenate behind; first valve 
- with five, last with two, middle with oneslit; teeth crenate, sharp, 
smooth; eaves minute; sinus deep, narrow; gills crowded with 
spicules, and with sutural pores. 
