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.-— -Te^f. Min. Rar. 5. t i. f. 16. 



EXTINCT SPECIES. 



1. P. /afesJOTa.— Nearly orbicular, flat, smooth, thin; umbo excen trie.— 

 Sower. Min. Conch, t. cxxxix, £ 1-5. — In Slaty Clay, Lincolnshire. 



2. P. /^rotor.— Depressed, conical, smooth, shining; base obovate; apex ex- 

 centric — Sower. Min. Conch, t. cxxxix. f. 3, 4 Alum Clay, Whitby. 



3. P. cBqualis. — 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 PateUite, 



Park. Or. Rem. iii. 50. t. v. f. 21 — 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 London 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. l.-— Lower Oolite, Stonefield. 



7. P. ancyloidis. — Convex, smooth ; apex spiral ; base ova\.— Sower. 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 Sand, 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. ^full. Zool. Dan. p. 250. No. 3017- Prtlt. Dorset, 

 25. Mont. Test. Brit. 6. 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 sununits ; 

 they are numerous on the sides of the plates, but not on the subcarinated 

 centre. The border is rough, with a spinous mai'gin. The tufts consist of 

 cylindrical, blunt, smooth, solid, calcareous spines of imequal size ; one at 

 the junction of each valve, six on the anteal margin, and two at the retral 

 valve, making twentv in number. — I am inclined to think that the Chiton 



