436 STOMOPNEUSTES. 



near the outer edge. Ocular plates broadly triangular, excluded from anal 

 system. Coloring of spines seems to be fully as variable as that of Eehino- 

 metra lucunter, with which it is always associated. 



Young specimens of this species show remarkable differences from the 

 young of Echinometra, reminding us somewhat of the changes undergone 

 by Arbacia. The spines of young are comparatively far shorter, stouter; 

 they are irregularly banded, so that, until a complete series was seen, the 

 young were supposed to belong to a distinct species. The granulation of the 

 abactinal system is also quite prominent in small specimens, measuring 6 mm - 

 longitudinal diameter, while in the largest specimens examined, measuring 

 20 nun, 3 the abactinal plates were nearly smooth. The contrast between the 

 comparatively huge spines and test is so great in the small specimens that 

 they would at first glance readily pass for young of Heterocentrotus trigo- 

 narius. 



Zanzibar; Kingsmills [stands; lionin Islands. 



STOMOPNEUSTES. 



Stomopneustes A<;.\ss., 1841. Munn<r. Scut. Int. 



This genus shows conclusively that the mere obliquity of the axis alone 

 is not a sufficient basis to form of the Echinometradae a family among the 

 Echinidae, as has been proposed by Gray. There are in Echinometra. in one 

 and the same species, specimens in which the elongation of the axis cannot 

 he traced, when we must depend upon the other characters of the genus. 

 Stomopneustes forms the passage between Strongylocefttrotus and the true 

 Echinometradae. The test is nearly circular, although then' is a slight ten- 

 dency to obliquity in the axis of old specimens. The spines are long, stout, 

 finely longitudinally striated. The actinal surface is Hat. the poriferous /.one 

 becoming petaloid ; while above the ambitus it is narrow, forming three irreg- 

 ular vertical lines of parallel rows of pores. The actinostome is small; 

 actinal cuts scarcely marked. There are but two principal rows of primary 

 tubercles, both in the ambulacra! and interainhulacral areas. 



By some oversight the name of Stomopneustes. given by Agassi/ to 

 Echinus variolaris, was overlooked in the Catalogue Raisonne ; and as Hclio- 

 cidaris, as there constituted, has become the receptacle for all doubtful 

 species, the i*estoration of this name cannot but prove justifiable, as the 



