28 ASPIDODIADEMA JACOBYI. 



a narrow irregular vertical line, separating the ambulacra! from the inter- 

 ambulacral region. The primary spines of the two areas are similar, those 

 of the ambulacral areas being smaller and more slender. The secondaries, 

 though not numerous, are remarkable for their uniform size in both areas, 

 and their arrangement recalls to a certain extent that of the papilla? of the 

 Cidaridse. In life the test is of a light greenish pink color, the areolas 

 darker; the secondary spines are of a light pinkish tint, darker at the base ; 

 the primary radioles yellowish green, with a greenish chocolate base. In 

 some specimens the test is also of this greenish chocolate color, the spines 

 more whitish, or tending towards a dirty yellow. 



The sheathed pedicellariae are most numerous above the ambitus toward 

 the abactinal region ; the shaft of the pedicellariae is nearly as long as that 

 of the secondary spines ; from then" size the sheathed pedicellariae are very 

 prominent objects on the test. 



The actinostome is covered by ten large buccal plates, as in A. riucrotuber- 

 culatum and A. aniiUamm, but these plates form a ring round the actinal open- 

 ing, leaving a bare ring between them and the edge of the test. 



There are eight large elliptical plates round the anal opening, somewhat 

 as in A. tonsum, but having a larger ring covered by minute plates between 

 them and the genital ring. The anal plates are closely tuberculated by 

 miliaries nearly of the same size as the miliaries of the ocular plates; the 

 genital plates are coarsely and closely tuberculated by miliaries. 



Smaller specimens differ from the larger ones mainly in the lighter coloring 

 of the test and spines, and the more Battened abactinal region of the test, 

 which loses its peculiar Echinostrephus-like shape as it increases in size, 

 becoming more regularly arched, as in Amblypneustes. The plates of the 

 actinal and anal system cover a comparatively larger space in younger 

 specimens. 



In a small specimen measuring about 3 mm., the anal plates appear as 

 forming close to the genital ring ; the difference in size of the genital and 

 ocular plates is already apparent. The anal proboscis is quite long at that 

 stage, equalling in length the diameter of the anal system. 



In a specimen measuring 28 mm. in diameter, the anal system measured 

 5.50 mm., the abactinal 10 mm., and the actinal 9 mm.; the height of the 

 test was 20 mm.; and there were eleven and twelve plates in the inter- 

 ambulacral ari 



In a specimen measuring 12 mm. in diameter, the anal system measured 



