288 
MOLLUSCA. BRANCHIFERA. Chiton. 
It is impossible to determine, from the scanty notices which are given by 
Walker, what was the true character of his P. plana orbiculata margine re- 
gulariter dentato. The colour white and opake.— Tes#, Min. Rar. 5. t i. f. 16. 
EXTINCT SPECIES. 
1. P. latissima . — Nearly orbicular, flat, smooth, thin; umbo excentric.— 
Sower. Min. Conch, t. cxxxix. f. 1-5. — In Slaty Clay.^ Lincolnshire. 
2. P. IcBvior. — ^Depressed, conical, smooth, shining ; base obovate ; apex ex- 
centric — Sower. Min. Conch, t. cxxxix. f. 3, 4 — Alum Clay., Whitby. 
3. P. wqualis — Conical, smooth ; base obovate ; back nearly perpendicular. 
— Sower. Min. Conch, t. cxxxix. f. 2 — In Crag., Suffolk. 
4. P. rugosa — Depressed, obovate, radiated ; apex excentric, depressed, 
slightly recurved ; back concave above, with reflected undulations — Patellite, 
Park. Or. Rem. iii. 50. t. v. f. 2\.-^Sower. Min. Conch, t. cxxxix. f. 6.-— 
In Lower Oolite., Gloucestershire. 
5. P. striata. — Oblong, irregularly conical, with numerous acute radii ; 
umbo forward, sharp — Sower. Min. Conch, t. ccclxxxix Lmdon Clay, Stub- 
bington. 
6. P. lata — Obovate, depressed, nearly smooth, radiated ; radii about 30. 
distant, rounded ; apex very excentric — Sower. Min Conch, t. cccclxxxiv. 
f. \.—-Lower Oolite, Stonefield. 
7. P. ancyloidis. — Convex, smooth ; apex spiral ; base oval.— .5'ower. Min. 
Conch, t. cccclxxxiv. f. 2 — Ancliff. 
8. P. nanus — Obliquely smooth ; base oval ; apex obtuse — Sower. Min. 
Conch, t. cccclxxxiv. f, 3 — AnclifF. 
Mr Mantell notices “ a small species of Patella of an oval shape, conical, 
depressed ; the casts of the interior of the shell only have been discovered” 
in Green Sa?id, Parham Park — Geol. Suss. 72. 
Gen. XLIII. CHITON. — Shell divided, constituting a series 
of imbricated dorsal plates, eight in number ; mouth with 
a semicircular curved membrane above, destitute of tenta- 
cula. Tongue short, armed with spines. 
* Marginal hand with tufts of spines. 
158. C. fascicularis . — Shell oblong, ovate, roughly shag- 
reened on the sides, with a striated longitudinal mesial stripe. 
Linn. Syst. i. 1106. Mull. Zool. Dan. p. 250. No. 3017. Pult. Dorset, 
25. 'Mont. Test. Brit. 5. t. xxvii. f. 5. — On oysters, but not com- 
mon. 
Length upwards of half an inch, breadth about a quarter ; freckled with 
green and brown. The granular tubercles are circular, with flat summits ; 
they are numerous on the sides of the plates, but not on the subcarinated 
centre. The border is rough, with a spinous margin. The tufts consist of 
cylindrical, blunt, smooth, solid, calcareous spines of unequal size ; one at 
the junction of each valve, six on the anteal margin, and two at the retral 
valve, making twenty in number. — I am inclined to think that the Chiton, 
