CHITONIDA. 343 
cHIToN, Lam. Girdle covered with distinct scales; anterior 
and posterior valves with many slits, middle valve with one; 
teeth blunt, serrate; eaves short, spongy; sinus squared, den- 
ticulate ; gills ambient. 
RADSIA, Gray. Teeth in middle valve two or more; differs 
also from Chiton in having side-slits. C. Barnesii. 
TONICIA, Gray. Anterior and posterior valves with many slits, 
middle with one; teeth sharp, serrate; eaves short, spongy; 
sinus squared, denticulate; girdle smooth or downy; gills en- 
circling. C. elegans, Fremb. (1xxxv, 80). 
FANNETTIA, Dall. Insertion-plates regular, branching ; middle 
valve with one,anterior and posterior with nine slits ; teeth sharp, 
serrate, long; eaves very short, sinus squared, denticulate; 
girdle smooth, spreading; gills encircling. 
EUDOXOCHITON, Shutt. Insertion-plates unfissured; teeth blunt, 
fimbriate; eaves short; sinus small, lamine united; girdle hairy. 
CRASPEDOCHITON, Shutt. Insertion-plates regular; middle valve 
with one slit, anterior with tive, posterior with eight; girdle very 
minutely asperulate. The posterior valve is fimbriated in the 
middle. A doubtful group. 
D. Acanthoidea. 
Insertion-plates thrown forward. 
‘* 
*K 
Plates broad, pectinated. 
SCLEROCHITON, Cpr. Zone as in Enoplochiton; laminz obtuse, 
pectinate ; sinus waved, smooth. Most like Enoplochiton, from 
which it differs in the articulation of the tail-plate and the sub- 
central mucro. 
** Plates sharp, grooved outside. 
ACANTHOPLEURA, Guilding. (Lucia, Gould.) Anterior and 
posterior valves with many slits, middle with one; teeth blunt, 
grooved; eaves projecting, grooved; sinus large, waved ; girdle 
with calcareous bristles. C. spiniger, Sowb. (Ixxxvi, 94). 
FRANCISIA, Carp. Valves partly immersed, planate; central 
laminz with several slits; sinus lobed. Bears the same relation 
to Acanthopleura that Fannettia does to Tonicia, with tlhe 
additional peculiarity of Radsioid nicks in the central valves. 
C. spinosus, Brug. (1xxxv, 81). 
* * * Plates sharp, smooth. 
DINOPLAX, Carpenter. Armor heavy, alate; mucro not ele 
vated, submedian; laminze separate, acute, smooth; last valve 
extending forwards; sinus small; girdle coriaceous, spinulose 
in fascicles. C. gigas, Linn. (Ixxxv, 88). 
MIDDENDORFIA, Cpr. (Dawsonia, Cpr.) Armor and girdle as 
in Acanthopleura; lamine acute, rugose exteriorly ; the sinus 
planate, not laminated. C. Polit, Phil. 
