28 THE VOYAGE OF H.M.S. CHALLENGES. 



anterior laminae very dark brown. In C. the sutural laminae are paler anteriorly, the rim 

 being nearly white. 



The number of slits is too variable to make them of any value for descriptive purposes. 



The shell of Acanthopleura granulata is ornamented with tubercles of fair size, which 

 on the jugum become much smaller, and arranged in more or less regular concentric lines. 

 There is a brown band on the jugum, separated from the greyish or brown sides by a 

 narrow white band ; the colour, however, is very variable, and may be lighter or darker ; 

 the anterior and posterior valves often have a dark lateral band. 



The shell of Acanthopleura sp., C, is too rubbed to determine accurately ; certainly 

 with tubercles on the lateral portion of the intermediate valves and on the terminal 

 valves ; the dorsal aspect of the intermediate valves apparently smooth, with concentric 

 lines of growth ; colour pale buff, with a darker band along the jugum and at the sides. 



Girdle. — Acanthopleura granulata, A. and B., crowded spines of variable thickness, a 

 great number being considerably larger than the others : the usual arrangement of bands 

 being a lateral black band for each of the first two valves, a broad black band for the fifth 

 and sixth, and one for the eighth — or four bands on each side ; the interspaces being 

 greyish, with occasional patches of black, the most constant of which is a variable band 

 opposite the seventh valve. Acanthopleura sp., C, the spines are much finer, shorter, 

 and more uniform than in the former. There is a lateral black band for each of the first, 

 second, seventh, and eighth valves, a broad band for the fifth and sixth, and traces for the 

 third and fourth. The shells and girdles of Acanthopleura spiniger and Acanthopleura 

 incana have already been described. 



In all the West Indian forms the spines extend from the girdle as a narrow band 

 between the valves ; this can, however, only be seen after the removal of the valves. 

 The same occurs in Acanthopleura spiniger (Challenger), but not in quite so marked a 

 degree, and not at all in the Red Sea specimens, nor in Acanthopleura incana. 



From the above analyses it seems clear that there are at least two species of the West 

 Indian Acanthopleura. 



In Gmelin's edition of the Systema Naturae, two closely allied species are described on 

 p. 3205, viz., No. 16, Chiton granulatus: " Ch. piceus supra planus, punctis elevatis 

 numerosis in Beries digestis, limbo lato coriaceo spinoso : areis nigris albisque alternis. 

 Chemnitz, Conchyl., vol. viii. pi. xcvi. fig. 806. Habitat in Oceano americano, valvis 8, 

 rarius 7." No. 17, Chiton piceus : " Ch. testa octovalvi supra glabra picea nigro albidoque 

 varia. Chemnitz, Conchyl., vol. viii. pi. xcvi. figs. 807-810; Chemnitz, Chit., pi. ii. 

 figs. 6, 6 a, b, c. Habitat in Mari americano et rubro, granulato affinis, intus medio niger, 

 ad latera virescens, maculis dorsi nigris et maculis fasciis venisque albidis aut virescentibus 

 alternis, valvis rarius, 7 aut 6." 



Gmelin considered these as distinct species, but the smoothness of the surface of the latter 

 was almost certainly simply the result of erosion. The coloration of the under surface 



