20 HEMIARTHRUM. 



H. SETULOSUM Carpenter. PI. 5, figs. 89-100 ; 1-8. 



The color of the shell is a uniform warm dark brown, and the 

 girdle is chestnut brown, with a pale crenulated border round the 

 margin of the valves. In each of the dark triangular bays between 

 the valves is a small tuft of short white spicular scales, and there are 

 six similar tufts round the anterior border of the first valve. The 

 anterior and posterior valves and the lateral areas of the inter- 

 mediate valves are marked by concentric lines of growth, otherwise 

 the latter are scarcely discernible. The jugum is very gently 

 rounded, so that the pleura are slightly depressed. The unslit in- 

 sertion plate of the anterior and posterior valves is shown in figs. 

 90, 94, and 4, 5, 6. The girdle (fig. 98) is thick and soft, with a 

 few minute scattered scales. There is a distinct fringe of reddish 

 brown elongated striated scales round the margin. The scales 

 forming the tufts are stout, and white in color. Carpenter describes 

 the anterior tufts as about four in number ; in my specimen there 

 are six anterior tufts. Evidently Carpenter was not quite satisfied 

 on this point, as in all other Chitons which possess tufts, only four 

 are present; and, consequently, that number might be expected to 

 occur in this species also. The head lappets are rather large, and 

 the anus is on a large rounded papilla. The longitudinal band on 

 the under side of the girdle (veil of Carpenter) is produced into flaps 

 at the posterior extremity. 



The gills (pi. 5, figs. 1, 99, 100, 7), form a short posterior row, 

 and appear to be about six in number ; they decrease in size anttr- 

 iorly. 



Length 9 mm. ; breadth 4 mm. ; side of valves meet at an angle 

 of about 115. (Haddon.') 



Length 13, width 7 mill. (Q>r.) 



Kerguelen Island, on stones at low water (Kidder); and Royal 

 Sound on shore (' Challenger ') ; South Georgia (Pffr). 



Hemiarthrum setulosum CARPENTER MS., p. 13. DALL, Bull. U. 

 S. Nat. Mus. ii, 1876, p. 44. HADDON, ' Challenger ' Polyplacophora, 

 p. 14, t. 1, f. 4; t. 2, f. 4a-l. MARTENS and PFEFFER, Jahrb. der 

 Hamburgischen AVissenschaftlichen Austalten iii, p. 108, t. 3, f. 4, 

 1886. 



The specimens from S. Georgia were much eroded ; they meas- 

 ured about 8-11 mill., and were when alive, "brown-black almost 

 black. " One of these is figured on pi. 5, figs. 1, 2, 3. 



