166 



PANAMIC DEEP SEA ECHINI. 



miliaries, and by far the greater number of them only traces of the prima- 

 ries (Pis. 81, fig. 2; 82; 83, fig. .' ; 84). When seen in profile (PI. 84, fig. ..') 

 there are not more than fifteen to sixteen prominent primary tubercles; 

 all the others as well as many of the miliaries have been resorbed. Seen 

 facing the anal system (PI. 84, fig. /) there are fifteen to sixteen irregularly 

 scattered in the odd posterior interambulacrum. 



An enlarged figure of a part of the ambitus and of the adjoining coronal 

 plates (PI. 80, fig. /) shows the contrast between the primary and miliary 



a m 8 





Outside. 95 inm. 



Fig. 238. Pilematechinus Rathbuni. 



InBide. 85 mm. 



Fig. 239. Pilematechinus Rathbuni. 



tuberculation of the former and that of the latter, on the plates of which we 

 find patches of miliaries only, large bare areas, and parts of the scrobicular 

 ring or indications of its former existence, or parts of the mammary boss in 

 all stages of resorption. Phis is still better shown in Plate 86, . fig. 2, on 

 the fifth and sixth right anterior interambulacral plates from the actinostome 

 and on the seventh plate of the right posterior interambulacrum. 



This resorption of the primary tubercles seems to be quite general among 

 many of the abyssal species of Spatangoids. See also Paleopneustes cristatus 

 (Pis. 95; 96, fig. 5), Paleopneustes hystrix (PI. 97, fig. 1), and Linopneustes 

 (PI. 93, fig. 1). 



Seen in profile (Pis. 82, fig. 1 ; 84, fig. ..') the anterior extremity slopes 

 quite regularly between the rounded abactinal part of the (est and the some- 



