REPORT ON THE ECHINOIDEA MORTENSEN" 



247 



The primary spines at the ambitus are not very long, the longest 

 preserved being only about 100 mm. in length by a thickness of 3.5 

 mm., not tapering. Possibly there may have been a few slightly 

 longer, but it may be said with certainty that the longest can only 

 very slightly have exceeded 1 Yi h. d. In the present specimen the 

 upper spines taper to a point and are much shorter than those at the 

 ambitus, though fully developed, as is evident from the character of 

 their surface, which means that the specimen has reached its full size. 

 The spines are perfectly smooth, shining, at most with a pair of in- 

 distinct longitudinal ridges, without any serrations. Even under the 

 microscope no longitudinal striation is to be observed. The collar 

 is short, 3-4 mm. in length, widening toward the milled ring. The 

 oral primaries are of the typical form, curved, strongly serrate, with 

 a smooth point, ending abruptly, not bifid as may be the case in some 

 species (elegans, acutispina) ; but this may be due to the point being 

 worn. The two proximal ones are fairly broad, the third is more slen- 

 der, and the fourth is only 

 recognizable as an oral pri- 

 mary through its strong 

 lateral serration; the fifth 

 and sixth still carry some 

 small lateral serrations, 

 being transitional forms. 

 From the third onward the 

 spines have the point 

 slightly widened, longitud- 

 inally serrate, ending ab- 

 ruptly as if worn off. This 

 also holds good for the 

 longest spines at the ambitus, which are directed downward, partly 

 even slightly curved. Evidently the animal has been walking on the 

 points of all these spines, only the shorter spines above the ambitus 

 being directed upwards. * 



The secondary spines surrounding the primaries are fairly robust, 

 about 12 mm. long, broad, distinctly excavate on the outside, espe- 

 cially toward the end, which is not at all or only slightly narrowed. 

 (PI. 76, figs. 1-2.) This excavation is especially conspicuous on the 

 spines below the ambitus. The ambulacral spines are about 8-10 mm. 

 long, very slender, almost setaceous, and erect. 



The pedicellariae have the heads about 5 mm. long; the valves (pi. 

 76, fig. 3) are slender, the blade being filled with the usual meshwork, 

 with no depression above the apophysis. The smaller forms are not 

 peculiar, all transition stages being found between the large and the 

 small ones. 



The spicules of the tube feet are rather small more or less fenes. 

 trated rods, and are irregularly scattered. Toward the end of the 

 tube feet they become somewhat larger fenestrated plates. (Fig. 3.) 

 27566—27 2 



Fig. : 



-Spicules from tube feet of Histocidaris mag- 

 nifica, new species. x240 



