STRONGYLOCENTROTUS INTERMEDIUS. 445 



of primary tubercles, flanked by somewhat smaller vertical rows, — one 

 between the principal rows and the poriferous zone, the other towards the 

 median line, — in small specimens the two median rows form an irregular 

 median line. Botli in the ambulacral and the interambulacral region large 

 miliaries fill the coronal plates in both areas ; they are arranged in regular 

 rectangles round the primary and secondary tubercles. The spines are 

 moderately long, slender, finely striated longitudinally. When dry, their 

 2olor is olive-green, frequently tipped with purple. The ground-color of 

 test is grayish, with more or less of a greenish tinge. The genital plates 

 are broader than long, forming a narrow ring round the large anal system, 

 the greater part of which is occupied by the opening left for the passage of 

 the claws of the parasitic crab. The genital plates are not all united later- 

 ally, three of the ocular plates extending to the anal SA'stem. On the actinal 

 side the test is quite flat, and adjoining actinal membrane the poriferous 

 zone is not unfrequently slightly petaloid. 



In large specimens there is less difference in size between the vertical 

 rows of primary and secondary tubercles, the interambulacral area being 

 occupied by fewer vertical rows of nearly equal sized tubercles ; spines also 

 become stouter in proportion ; the anal system is less sunken, and the abac- 

 tinal part of the test is much less distorted, even when attacked by the para- 

 sitic crab. In a few specimens in alcohol in the Jardin des Plantes and in 

 the Museum Godeffroy I could see no trace of the opening for the parasitic 

 crab. The abactinal was sunken, though but little, and the upper part of 

 the test was not asymmetrical, otherwise these specimens free from the 

 parasites showed no further differences, and were fully as gibbous and pen- 

 tagonal in outline as specimens attacked by parasite. The actinal system is 

 small, the cuts very slight. 



Chili ; Galapagos ; Peru. 



Strongylocentrotus intermedins 



! Psammechinus intermedius Barn., 1863, in A. Ac, Proc. Ac. N. S. Phila. 

 ! Strongylocentrotus intermedius A. AG., 1872, Rev. Ecli., Pt. I. p. 164. 



Outline from above pentagonal; test depressed. Poriferous zone broad, 

 nearly as broad as the median ambulacral space ; this is flanked by two 



