278 STRONGYLOCENTROTUS DROBACHIENSIS. 



and can readily see how with small series it would be possible to establish the 

 species generally recognized as S. chlorocentrotus, S. granulans (granulatus 

 Gould). Careful measurements of a number of specimens of the alleged 

 species are here given, tabulated according to their origin, and fail to show 

 any characters by which they can be separated. 



The thickness of the test is extremely variable, the specimens from the 

 northwest coast generally are very much thinner (chlorocentrotus), though 

 those which are known as carnosus are more like Drobachiensis, and have a 

 somewhat thicker shell, while in granulatus it is often quite thick. The shape 

 and outline are very variable, as seen from measurements. Coronal plates are 

 of median height, with but one large tubercle on each plate, forming the two 

 principal vertical rows of the interainbulacral space, the rest of the plate 

 being closely covered by secondaries, so as to form irregular vertical or 

 transverse lines, as is usually the case in granulatus ; or the vertical lines are 

 more regular (as in Drobachiensis), the secondaries being larger and the 

 smaller secondaries less prominent, these being the greatest extremes. The 

 same general features of arrangement hold good in ambulacra! and inter- 

 ambulacral spaces. Though the extremes have been mentioned, we find the 

 loose arrangement of granulatus combined with the thin and thick test, and 

 with the broad and narrow poriferous zone. The arcs of pores of granulatus 

 are straighter, but in Drobachiensis said to be more vertical. This depends 

 upon the height of the vertical plates; when arcs are straight, the poriferous 

 zones are separated by two irregular oblique rows of minute tubercles which 

 follow the curve of the poriferous zones. The number of pairs of pores varies 

 greatly; in one and the same specimen we find one zone with six pores near 

 ambitus and generally but five above it, when in the next zone there may 

 be five or six above as a general thing. 



Of the ocular plates two reach the anal system and the others are excluded. 

 The madreporic body is very much larger than other genital plates, which are 

 short-sided near the anal system, and long, pointed, extending beyond the level 

 of the ocular plates, with pretty large genital openings. Secondaries covering 

 loosely the whole abactinal system ; anal system large ; exterior row of plates 

 largest, gradually diminishing towards anus. Spines vary greatly in length, 

 comparatively slender, greenish-purple, or violet, or flesh-colored, or even 

 cream-color. Buccal membrane thin, with few small plates irregularly placed 

 in continuation of ambulacral system. Auricles slight, with large opening ; 

 shallow ridge connecting them. 



