70 ISCHNOCHITON. 



Chiton variegatus PHIL., Enum. Moll. Sicil. i, p. 107, 1836; ii, p. 

 83, t. 19, f. 13. WEINKAUFF, Conchyl. des Mittelm. ii, p. 412. 

 ISSEL, Chit, del mare di Geneva, Bull. Mai. Ital. iii, p. 7, t. 1, f. 1, 

 1870. Chiton marginatus Perm., TIBERI, Bull. Soc. Mai. Ital. iii, 

 p. 139, 154. MONTEROSATO, Enum. e Synon. p. 16, 1878. BUQ,, 

 DAUTZ. & DOLLF., Moll. Mar. Rouss. i, p. 497, t. 61, f. 13-16; t. 

 62, f. 3. 



I have preferred to retain the Mediterranean form distinct, at 

 least as a geographic variety, for it differs from Tr. cinereus of the 

 north in being constantly smaller, having fewer slits in the end 

 valves, and having the sutural plates of a decidedly different shape. 



I. ALBUS Linne. PI. 7, figs. 35-38. 



Shell oblong, elevated, the back keeled, lateral slopes nearly 

 straight. Anterior valve half-circular, its posterior margin slightly 

 concave ; sculpture consisting of some scarcely perceptible, low 

 radiating ridges, often wholly obsolete, and an excessively minute 

 shagreening or granulation of the whole surface, the granules 

 showing a disposition to be arranged in oblique curved lines. 

 Intermediate valves slightly beaked, produced forward in the mid- 

 dle, having the same sculpture, and showing low, irregular growth 

 wrinkles. Lateral areas scarcely raised, sculptured like the front 

 valve. Posterior valve having the umbo slightly elevated, central, 

 inclined backward. 



Interior white. Sutural plates large and wide, extending from 

 the insertion plates nearly to the jugum. Sinus rounded. 



The anterior valve has 13 slits in the smooth and rather sharp 

 insertion plate ; the intermediate valves have one slit ; the posterior 

 valve has 10 slits, and the edge of the plate is decidedly roughened 

 and irregular. Another specimen has 14 slits in the anterior valve, 

 12 in posterior valve; and in still another individual, some of the 

 intermediate valves have two slits on one side. 



The girdle is covered with small gravelly scales, and has no 

 marginal fringe of long scales or spines. 



The gills consist of thirteen leaflets on each side, extending for- 

 ward two-thirds the entire length of the foot. 



The color is a very delicate buff tint, sometimes almost white, 

 often shading into a light orange on the posterior part and lateral 

 areas of each valve. Most specimens have more or less of a black 

 deposit on the back part of the valves. 



Length 15, breadth 7 mill. 



Length 10, breadth 5-6 mill. 



