PHYLLACANTHUS DUBIA. 389 



whole surface of abactinal system sparsely covered by miliaries. One row 

 of large plates round the anal system extending between the genital plates 

 to ocular plates ; interior plates of anal system irregular in shape, few 

 in number, diminishing gradually in size towards anal opening. 



Secondary spines and papillae long. Primary spines extremely variable 

 in shape, from flattened, spindle-shaped spines with serrated edges, slender at 

 base and pointed at extremity, to a uniformly tapering cylindrical shaft 

 with regular longitudinal rows of granulation. The character of the spines 

 gives such a different appearance to specimens that it is not remarkable 

 that many species should have been based upon features of such striking 

 character ; the only figures we possessed, that of Savigny and that of Miche- 

 lin, of the two extremes, naturally only strengthening the belief in the 

 validity of the differences noticed. A remarkably fine series of the varia- 

 tions of this species, due to the changeable nature of the spines, exists in 

 the Stuttgart Museum ; the only positive character of permanence being the 

 spotted base of the shaft of the spine below the milled ring, which is of a 

 light reddish or reddish-yellow ground-color, with deep violet spots marked 

 extremely distinctly upon the fine longitudinal striation. No matter what 

 might be the structure of the spine, the groundwork of granulation remained 

 the same, and could be distinctly traced either when the primary spines were 

 ornamented by thick lamellae running longitudinally, or were irregularly 

 covered by short spines, or were spindle-shaped with serrated edges, or 

 simply cylindrical shafts, slightly fluted. 



Red Sea; Mauritius; Zanzibar. 



Phyllacanthus dubia 



FhyUacanthus dubia Br. 1835, Prod. Des. An. 



PI. P.f. 39; PL I'.f. 7-10; PI F.f. 1, 2. 



This species is extremely closely allied to P. imperialis, but better series 

 of specimens than those thus far collected may yet show the identity of this 

 species with P. imperialis. The geographical range of the two species is 

 nearly identical; the characters enumerated below have, ho\v T ever, been 

 found to be permanent. 



Genital openings large, on the very outer edge of the genital plate, placed 

 in a well-marked groove ; granulation of abactinal system coarse ; ocular 

 plates smaller, and plates of anal system larger and less numerous than in 

 P. imperialis. 



