22 CHITON. 
quivalve, irregular, thick, foliaceous, attached by the umbo of 
the lower and larger valve. External ligament placed in a 
groove, following the involution of the umbones. Umbones 
spiral, coiled round on the back of the valves; hinge witha 
thick, crenated, lengthened tooth, in one valve, entering a cor- 
responding cavity in the hinge lamina of the other; muscular 
impressions two in each valve, distant, lateral. Obs. Diceras 
may be known from Chama, by the spiral horns into which the 
umbones are produced; Isocardia, by the regularity of the shell; 
and it is hardly necessary to mention Spondylus, which may be 
known by the triangular disc between the umbones; Cleido- 
theerus, Stutch. which resembles Chama in general form, has a 
separate bony appendage attached to the hinge, and may more- 
over be known by its elongated muscular impression. Fig. 153, 
C. Lazarus. 
CHAMA’CEA. Bl. The seventh family of the order Lamelli- 
branchiata, Bl. containing the genera Chama, Diceras, Etheria, 
Tridacna, Isocardia, Trigonia. 
CHAMBERED. When the cavity of a shell is not continuous, 
but is divided by shelly diaphragms or septa, it is said to be 
chambered. This disposition is frequent in the Cephalopods 
and gives rise to the distinction of Polythalamia, but it is not 
confined to them as it occurs in some species of Chama, and in 
some vermicular shells and turrited univalves, &c. 
CHA’RYBS. Montf. A genus of microsopic Foraminifera. 
CHELONO’BIA. Leach. Coronula Testudinaria, Auct. Fig 15. 
CHICO’REUS. Montf. A generic division of the genus Murex, 
consisting of such species as have three ramified varices. Ez. 
M. Inflatus, fig. 395. 
CHILINA. Gray. Fam. Auriculacea, Bl. Colimacea, Lam. 
Descr. Oval, thin, covered with an olive green epidermis; spire 
rather short, consisting of few whorls; aperture large, oval, 
rounded anteriorly; outer lip thin, joining the inner lip without _ 
a sinus; inner lip spread over part of the body whorl, termina- 
ting in a thick columella with one or two folds. Obs. These 
shells differ from the true Auriculz in the thinness of the outer 
lip. C. Dombeyana, (Auricula Dombeyana, Auct.) Fig. 300. 
CHIMOTREMA. Montf. Belongs to Herix, Auct. 
CHIONE. Megerle. Cytherzea Maculata, (fig. 117. c.) Sulcata, 
Circinata, &c. Auct. and other similar species, 
CHISMOBRANCHIA’TA. Bl. Second order of first section of 
Paracephalophora Monoica, Bl. containing ear-shaped, partly 
internal, spiral univalves. Gen. Coriocella, Sigaretus, Cryp- 
tostoma, Oxinoe, Stomatella, and-Velutina. 
CHI'TON. Lam. (X:rov,an integument.) Fam. Phyllidiana, 
Lam. Class. Polyplaxiphora, Bl. Deser. Oval, consisting of 
eight arcuated valves, arranged in a transverse series across the 
body of the animal, set in the skin, which forms a rim around 
