MARINE MOLLUSCA OF THE UNITED STATES. ; 97 
3. D. priocenuM, Toumey and Holmes. Fig. 197. 
Pliocene Foss. So. Car., 105, t. 25, f. 2. 1857. 
Shell slightly curved, marked by about thirty-eight very indis- 
tinct ribs, which become obsolete towards the base; lines of 
growth numerous, indistinct; aperture orbicular. 
(Living?) South Carolina. 
Family CHITONID&. 
Head surrounded by a semicircular veil or hood; eyes and 
tentacles none; mouth with cartilaginous jaws; gills in a series 
of lamellae, between the mantle and foot round the sides and pos- 
terior part of the body; foot oblong, rounded at each end.  Lin- 
gual ribbon long and linear, with numerous transverse series of 
teeth. 
The Chitons are abnormal mollusks in many respects. Their 
shell in eight separate but connected pieces gives them an articu- 
lated appearance; the heart is central; the reproductive organs 
symmetrical, with two orifices, and the sexes united; the intes- 
tine is straight, and the anal orifice posterior and median. 
Notwithstanding these resemblances to the annelids they are 
believed to be more closely related to the mollusca. 
Genus CHITON, Linnzus. 
Syst. Nat., edit. x. 1758. 
1. C. menpIcARIUS, Mighels and Adams. Fig. 198. 
Bost. Journ. Nat. Hist., iv. 42, t. 4, f. 8. 1842. 
C. Hanleyi, Bean. Thorpe’s Brit. Mar. Conch., 263. 1844. 
Shell cinereous, with dark clouds, long, oval with obtuse dorsal 
ridges; surface with elevated dots or granules, disposed in longi- 
tudinal lines, except towards the margin, where they are irregular 
and larger; no visible concentric striz ; triangular areas very in- 
distinct, outer whorls small, margin coriaceous, red. 
Length 25, breadth 10 mill. 
Maine, northwards. (Hur.) 
2. C. APICULATUS, Say. Fig. 199. 
American Conch., No. 7. 1834. 
Shell oblong-oval, convex; valves obtusely Parinate, the central 
portion of the posterior margins becoming slightly beaked with 
age. Lateral areas triangular, studded with numerous rounded 
tubercles, obsolete towards the apices, more numerous towards 
t 
