16 THE VOYAGE OF H.M.S. CHALLENGER 



Island of Plata, West Columbia; found on dead shells in 17 fathoms (Cuming; 

 Sowerby). 



The name Chiton roseus having been preoccupied by Blainville (Diet, des Sci. Nat., 

 1825, vol. xxxvi. p. 553), Sowerby 's name cannot stand. The fact that Blainville's species 

 is an Acanthochiton, while that of Sowerby is an Ischnochiton, does not affect the question, 

 since they were both described as Chiton roseus. I have therefore re-named this species 

 Ischnochiton boogii, as the specific names of Sowerbianus, Eeeve, and Watsonii, Sowerby, 

 are also preoccupied. 



The locality attributed, on the authority of Cuming, to this species, made the 

 identification with it of a Chiton from Fernaudo-Noronha very doubtful. A shallow- 

 water species was not likely to live in both the Atlantic off Brazil and in the Pacific off 

 West Columbia, with the whole breadth of South America between. That the Challenger 

 specimen is identical with the British Museum specimens is beyond doubt. May not the 

 difficulty find solution in the fact that the " I. of Plata," as it stands on Cuming's 

 tablet in the British Museum, and to which Sowerby (loc. cit.) added " W. Columbia," 

 is really some island in the estuary of La Plata ? 



The above criticism was first suggested to me by the Eev. R. Boog Watson, to whom 

 it gives me great pleasure to dedicate this species. 



The single specimen in the collection is of a pink colour mottled with creamy yellow, 

 with an obscure yellow line along the jugum, and with a pale spot on each side of the 

 line on several valves ; there are also several irregular dark patches ; the posterior valve 

 is deep-rose below the umbo. The girdle is mottled brown and white, there being a 

 white patch at the junction of each valve. 



The shell is long, narrow, and arched, anterior and posterior valves with fine con- 

 centric ridges ; the umbo of the latter is prominent. The intermediate valves are 

 apparently smooth, but really with extremely delicate longitudinal striae ; the lateral areas 

 are characterised by wide ridges. The ligament has stout, tall, imbricate scales. 



The three specimens of this species in the British Museum are pink and only slightly 

 flecked with white, no black or brown spots, and in two of them the central areas have 

 concentric lines like those of the lateral areas. 



Ischnochiton viridulus (Couthouy). 



Chiton viridulus, Couthouy MS. (Gould), Proc. Boston Soc. Nat. Hist., 1846, vol. ii. p. 144; Wilkes, 

 U.S. Explor. Exped., 1852, vol. xii. p. 318 ; Otia, 1862, p. 5. 



Habitat. — Cape Town. 



Orange Harbour, Cape of Good Hope. 



Shell. — Of the single specimen uniformly covered with minute low tubercles, which 

 are horizontally disposed on the pleura ; lateral areas scarcely distinguishable ; the peri- 



