PLAXIPHORA. 317 



slight projection there ; the intervals bearing some indistinct radii. 

 Posterior valve depressed, the mucro inconspicuous and about at the 

 posterior fourth ; posterior area obsoletely radiately ribbed. 



Interior light blue-green. Sinus small and shallow. Sutural 

 plates low. Anterior valve having 8, central valves 1 slit; the slits 

 short, continued in grooves to the eaves; teeth long, irregularly 

 striated outside, thickest along the slits, sharp edged. Posterior 

 valve having the insertion-plate long and stout at the sides, inter- 

 rupted by a rounded sinus in the middle behind ; its edge smooth, 

 unslit. Eaves very narrow and very spongy. 



Girdle rather wide, leathery, having at each suture a small pore 

 bearing several long corneous bristles, and with one or two more or 

 less irregular series of bristle-bearing pores on the surface of the 

 girdle, and a more or less dense clothing of small soft hairs over its 

 outer part. 



Length 50, breadth 35 mill.; divergence 125-135. 



Chiton setiger KING, Zoological Journal v, p. 338 (1831). Sow- 

 ERBY, Conch. Illustr., f. 17 ; Zool. Beechey's Voy., pi. 40, f. 7 (bad). 

 REEVE, Conch. Icon. t. ix, f. 48a, t. xiv, f. 48c. GOULD, U. S. 

 Expl. Exped., Moll., p. 330, f. 425. Plaxiphora carmichaelis GRAY, 

 P. Z. S. 1847, p. 68, and subsequent writings, probably not Chiton 

 carmichaelis GRAY, Spic. Zool. 1828. Plaxiphora carmichaelis 

 HADDON, Challenger Keport, Polyplac., p. 32. H. & A. AD., Gen. 

 Rec. Moll, i, p. 481 ; iii, t. 55, f. 3. Chcetopleura savatieri ROCHE- 

 BRUNE, Bull. Soc. Philomathique de Paris, 1880-1881, p. 119 ; 

 Miss. Sci. du Cap Horn, Polyplacophores, p. 135, t. 9, f. 3a, 3b. 

 Chcetopleura frigida ROCHEBR., Miss. Sci. du Cap Horn, p. 137, t. 9, 

 f. 5a, 5b. (young shell.) 



This is the only well-established species known to inhabit the 

 extremity of South America. It will be readily recognized by the 

 smoothness of the surface, strong diagonal rib, and generally well- 

 defined sutural pores, each bearing several bristles. The variation 

 in color is well-shown on the plate. The C. savatieri (pi. 67, figs. 

 41, 42), and C. frigida (pi. 67, figs. 39, 40) of Rochebrune are 

 merely, it seems to me, individual mutations of setiger the last being 

 a young shell. It will not escape the observant zoologist that the 

 artist who drew the plate of Chitons illustrating Rochebrune's paper, 

 did not see the lateral slits in the valves. One is likely to infer that 

 the other characters may be equally erroneously represented. 



Some authors have given Gray's name carmichaelis to this species ; 



