STOMOPNEUSTES VARIOLARIS. 437 



species subsequently added to Heliocidaris have only increased the confusion 

 already existing in the genus. 



Stomopneustes variolaris 



! Echinus variolaris Lamk., 1816, An. ?. Vert. 



! Stomopneustes variolaris Agass, 1841, Monog. Scut. Int. 



PllV.f. i-s ; PL XXIV. f. 31 -32; PI. VI. f. n-if; PI XXXVI. f, 2, s. 



The general aspect of the test of this species with its spines is that of 

 some varieties of Heterocentrotus trigonarius, with more slender and nu- 

 merous spines. The test is thick; more or less irregular in outline when 

 seen from above, according to the greater or less eccentricity of the axis ; 

 the auricles very slender, somewhat depressed. Abactinal system compact ; 

 anal system tolerably large, thickly covered by small plates, carrying sec- 

 ondary tubercles ; the genital and ocular plates each carry one secondary 

 and smaller miliaries. Madreporic genital large ; the genital ring narrow, 

 all the plates nearly uniform in size. 



The denuded test can at once be recognized by the continuous groove 

 extending along the vertical suture of the plates in the median interambu- 

 lacral space. This groove is barely marked in the ambulacral region. The 

 coronal plates are high ; two principal vertical rows of primary tubercles in 

 the ambulacral and interambulacral spaces, the ambulacral but slightly 

 smaller than the interambulacral. The ambulacral plates are loosely covered 

 by large secondaries and irregularly arranged miliaries extending into the 

 poriferous zone. The poriferous zone is separated from the primary rows 

 of tubercles by a vertical row of small tubercles ; two median interambu- 

 lacral vertical rows of small tubercles, irregularly arranged, separate the 

 primary rows above the median space. 



The actinostome is small ; branchial notches moderately marked ; tuber- 

 cles of actinal surface small, but rapidly increasing towards the ambitus. 

 Principal spines are stout, solid, tapering, coarsely striated longitudinally from 

 the prominent milled ring ; their color is olive green with purple tips. The 

 poriferous zone is narrow above the ambitus ; it is proportionally narrower in 

 older specimens, where, owing to the great flattening of the actinal surface, 

 the poriferous zone becomes extremely petaloid ; but the number of pores 

 in each arc is not increased, though adjoining arcs are crowded together 

 laterally in such a manner as to give all the appearance of a great number 

 of pores to each arc. In young specimens, as is seen by the measurements, 



