26 PANAMIC DEEP SEA ECHINI. 



The primary radioles and other spines early attain nearly their full 

 growth, specimens of 13 nun. in diameter already having radioles 51 mm. in 

 length. In the largest specimen examined, .'JO mm. in diameter, the longest 

 radiole was 75 mm.; the longest of the serrated radioles on the actinal 

 side was 2li mm. ; those immediately surrounding the actinal edge of the 

 interambulacral area varied in length from 5 to I'J. mm. In the same 

 specimen (30 mm. in diameter) the greatest diameter of the abactinal 

 system was 10 mm. ; the sides of the anal pentagon varied from 5 to 6 mm. 

 There were six and live primary interambulacral tubercles. In a specimen 

 of 10 mm. there are already four, with (races of a fifth ; in a specimen of 14 

 mm. there are four, with a fifth well advanced ; in one of 18 mm. there are 

 five, with traces of a sixtli ; in one of 23 mm. there are six and five, as in 

 the older specimens. 



The abactinal system (PI. 7, figs. 1-3) is crowded with small secondary 

 tubercles carrying papillae ranging in length from 1.5 mm. to 4 mm. They 

 are smallest on the anal system. They only differ from the secondary spines 

 of the interambulacra in length, those being at least 5 mm. long in the 

 equatorial region of the corona. Toward the actinal system they become 

 more spathiform and shorter, both in the ambulacra 1 and interambulacral 

 areas above the ambitus. As a whole, the ambulacra! papillae are shorter 

 than those of the interambulacral areas. 



In none of the specimens examined are the primary tubercles crenulate 

 (Pis. 8, tig. 7; 10, figs. 7, ;.\) but they all carry the characteristic smaller, 

 flattened, spear-shaped, serrated, primary actinal radioles characteristic of 

 the genus both in the fossil and recent species (PI. G, fig. 1). The angle of 

 the plates along the median interambulacral suture is usually bare of mili- 

 aries. The scrobicular circle is surrounded by a row of secondary tubercles 

 alternating with miliaries (Pis. 8, fig. 7; 10, fig. :.'), and the angular spaces 

 of the interambulacral plates, when not bare along the median line, are filled 

 with small secondaries and miliaries irregularly arranged. The secondaries 

 forming the median vertical row of the ambulacral system are arranged in 

 a single vertical line close to the median line of the ambulacrum ; in the 

 equatorial region of the test the ambulacral plates carry in addition one 

 or two miliaries below the secondary tubercle (PI. 10, fig. /). 



The actinal system of this species presents some marked peculiarities 

 (Pis. 7, fig. 6', 8, fig. ,~) ; we find the ambulacral buccal plates clustered 

 round the actinostome, separated by a wide zone from the ambulacral plates 



