ECHINOIDEA. I. 



87 



area is large, in S and young specimens slightly raised, in the adnlt $ so mnch raised as to form a 

 very conspicnons knob (PI. VII. Figs. i — 4). When both the peristome and the apical area are wanting, 

 the test resembles a little rine. 



All the measures are in millinietres. 



The interambulacral areas are abont twice as broad as the ambulacral ones; the boundaries 

 between the piates are very indistinct, especially in the ambulacral areas; they are given too distinctly 

 in the fignres (PL VIII. Figs. 24 — 25). Near the apical area the ambulacral piates are .single, farther 

 down they are coalesced in the common way, three and three. Here one larger tubercle is found for 

 each compound plate, and besides some qtiite small ones above each primary tubercle. The ambula- 

 cral piates are comparatively high, so that upon the whole the same number of ambulacral and inter- 

 ambulacral piates is found. The pores form almost a straight line, but are in reality trigeminate, 

 which faet, however, is not distinct in the upper part of the area; the upper hole of each pair of 

 pores is larger than the lower one. The interambulacral piates, especially above, are rather broad, the 

 horizontal boundary line between the piates bends downward in the middle; the median line of the 

 area is onlv slightly sinuate, likewise in the ambulacral areas. Each interambulacral plate has a not 

 very conspicuous primary tubercle near the sinuate lower edge and besides some miliary tubercles- 

 In S the upper piates are almost smooth, in J these piates are very richly provided with miliary 

 tubercles. In the adult J the test most frequently has an irregnlar, grooved-netshaped surface, espe- 

 cially between the close-set tubercles on the upper interambulacral piates. 



The primary .spines are in the adult specimens hardly as long as the diameter of the test, in 

 small specimens somewhat longer than the diameter; the spines around the mouth are somewhat curved 

 in the point. All the spines are strongly indented, and end in a little, conical point, surrounded by 

 ca. 6 smaller points (PI. VIII. Fig. 9); the actinal spines end irregularly truncate, presumably owing to 

 wear (PI. VIII. Fig. 17). In transverse sections (PI. XI. Fig. 6) the spines are seen to consist of 6 longi- 

 tudinal ridges the outer edge of which is somewhat widened; they are united with each other so as 

 to form a little cavity in the middle, and 6 smaller cavities in a circle round this. 



The buccal membrane is covered by large piates, which under the microscope are seen to be 

 common, almost smooth fenestrated piates. Those inside of the buccal piates are smaller and quite 

 smooth, and the piates decrease likewise in size towards the edge of the peristome (PI. VII. Fig.s. 11, 15). 

 The buccal piates are more complicate, and form a little arch, as it were, over the base of the tube 



