20 ON THE ECHINODERMATA OF THE 



1866. Euryethiniis granulatus, Terrill, Proceed. Boston Soc. Nat. Hist. vol. x. pp. 340, 352. 



1868. Toxopneustes pictus, Norman, Report Brit. Assoc. Adv. Sci. 1868, p. 314. 



1871. Toxopneustes pallidas, G. 0. Sara, Vidensk. Selsk. Forhandl., Nye Echinodermer, p. 25. 



1871. Toxopneustes drobachiensis, Loven, Ofvers. K. Vet.-Akad. Forhandl. 1871, no. 8. 



1872. Strongylocentrotus drobachiensis, A. Agassiz, Revision of the Echini, pp. 162, 277. 



1877. Strongylocentrotus dr'obachiensis, Marenzellor, Ccelent. Echin. u. Wiirmer d. ost.-ung. Nordpol- 

 Exped. pp. 3, 29 (Denksch. d. k. Akad. d. Wissensch. Wien, Bd. xxxv.). 



Test depressed, the height being proportional to the diameter as 1 : 2 approxi- 

 mately. Ambital outline almost circular, and only slightly subpentagonal ; contour of 

 the profile somewhat conoid, rounded at the apex. Test well rounded beneath, and 

 incurved towards the interior at the margin of the actinostome. Actinostome large, 

 and occupying three eighths or more of the diameter. Branchial notches very slight. 

 Buccal membrane thin, and with comparatively few small, granulated, oblong scales 

 and ten large buccal plates. Coronal plates comparatively high, each bearing one 

 large primary tubercle, imperforate and uncrenulate. The series of these tubercles form 

 two prominent vertical lines, which extend from the apex to the actinostome, both in 

 the ambulacral and in the interambulacral areas. In the interambulacral areas the 

 plates above the ambitus bear a number of miliary tubercles, which are disposed in an 

 irregular manner around the primary tubercle, and form not unfrequently in small spe- 

 cimens a more or less clearly defined scrobicular ring ; below the ambitus a secondary 

 tubercle is present on each side of the primary, and, in fair-sized specimens of the 

 Echinus, the external ones (which stand nearest to the poriferous zone) may be traced 

 upon the abactinal surface of the test, extending in very rapidly diminishing series for 

 some distance above the ambitus. In the ambulacral areas there is a small secondary 

 tubercle on each plate on the inner side of the primary tubercle, the series diminishing in 

 size as they approach the apex, in the neighbourhood of which the secondary tubercles 

 become altogether undistinguishable from the few other miliaries which are present 

 on the plate. Near the ambitus the miliaries are fairly numerous and irregular in size, 

 the most conspicuous amongst them frequently forming, on the pore side of the plate, 

 an arched row of three or four, which stands between the arc of pores and the tubercle, 

 the adoral miliaries being largest. The pores are arranged in arcs of 5-6, those above 

 the ambitus diverging only slightly from the vertical. The apical system is large, 

 and also the anal ring, into which two ocular plates enter. The madreporiform and its 

 companion anterior genital plate considerably exceed the other genital plates in size, 

 which are often not much larger than the two entering ocular plates. The genital 

 foramina are large. The spines are comparatively fine and delicate, and vary consider- 

 ably in length, which ranges from 8 to 13 millims. 



Colour. The colour of the test is a varying shade of purplish brown, that of the 

 spines greenish grey, the test being sometimes green in tint also. 



Size. The northern specimens are comparatively smaller than individuals from a 

 more southern habitat. The largest example obtained during Sir George Nares's expe- 

 dition was taken at Cape Napoleon, and measures 43 millims. in diameter, 21 millims. 

 in height, and has 20 primary interambulacral tubercles. 



