ISCHNOCHITON. 103 



each valve. The umbo of the posterior valve is central and mod- 

 erately elevated. 



Interior white ; sutural plates small, separated by a very wtdep- 

 flat sinus. Anterior valve having 13, posterior valve 10 slits, cen- 

 tral valves 1 slit ; teeth sharp ; eaves narrow, short, solid. 



Girdle covered with close, very small, striatulate, imbricating 

 scales. Length 15, breadth 8 mill. 



Mediterranean and Adriatic Seas. 



Chiton rissoi PAYR., Moll. Corse, p. 87, t. 3, f. 4, 5 (1826). 

 PHILIPPI, Enum. Moll. Sicil. i. p. 107. CAPELLINI, Journ. de 

 Conchyl. (2) iii, p. 322 (1859). ISSEL, Intorno ai Chiton del mare 

 di Geneva, in Bullettino Malacologico Italiano, iii, p. 5, t. 1, f. 2, 3 

 (1870). MONTEROSATO, Journ. de Conchyl. 1878, p. 147. BUQ., 

 DAUTZ. & DOLLF., Moll. Mar. Kouss. p. 495, t. 61, f. 10, 11, 12 ; t. 

 62, f. 2. Ch. meneghinii CAPELLINI, Journ. de Conchyl. (2) iii, p. 

 325, t. 12, f. l. Ch. mediterraneus "Gray MS." REEVE, Conch. 

 Icon. t. 23, f. 157 (1847). 



This species is well characterized by its flat close concentric rib- 

 lets and the sparsely scattered snowy spots on the end valves and 

 lateral areas. The sculpture of the lateral areas is irregular and 

 variable, the riblets being ragged-edged and occasionally subobso- 

 lete, leaving the raised areas almost smooth. The C. polii Phil, is 

 readily distinguished from this species by its differently formed 

 posterior insertion teeth ; in rissoi the posterior teeth are normally 

 Ischnoid. 



The Ch. mediterraneus of Reeve is simply a synonym of the typi- 

 cal form of this species. The form which Reeve calls rissoi (C. 

 Icon. t. 19, fig. 122) is a synonym of the variety meneghinii. 



Var. meneghinii Capellini (pi. 20, figs. 8-10). Sculpture stronger, 

 the end valves and lateral areas exhibiting distinct radiating striae. 



Var. fragilix Monts. (Enum. e Sinon.). Smaller in size, the 

 sculpture obsolete, without trace of radiating strise. 



I. PERTUSUS Reeve. PI. 20, figs. 18, 1 9. 



Shell oblong-ovate, valves elevated in the middle, verv closely 

 grooved throughout, ridges of the central areas thin, converging 

 towards the umbones, interstitial grooves pricked, posterior edge of 

 the valve serrated ; dark red, sprinkled with a few minute white 

 dots ; ligament horny, very sparingly beset with short bristles. 

 (Jfoe.) 



