ECHINUS TYLODES. 2G9 



Echinus atlanticus Mrtsn. 



Echinus atlanticus Mortensen, 1903 "Ingolf " Ech., pt. 1, p. 101. 



Plate 110, figs. 1-3. 



As no figures of this fine species have ever been pubhshed, it seems worth 

 while to give illustrations showing the general appearance. The specimen 

 figured is from the type locality, "Challenger" St. 34.3, off Ascension Island, 

 Atlantic Ocean, 425 fathoms. 



Echinus tylodes/ sp. nov. 

 Plates 93, figs. 11-15; 109, figs. 1-3. 



Although there are but two specimens, and one of those quite young, I feel 

 little hesitation in naming this new species. The type (PI. 109, figs. 1-3) is 

 57 mm. in diameter and 39 mm. high, with an abactinal system 13 mm. across 

 and an actinostome 19 mm. in diameter. There are 17 interambulacral, and 23 

 ambulacral plates in each column. The longest primary spines are only 18 mm. 

 long. The test is well arched, thick, and rough. The roughness is due to all 

 the tubercles being more or less elevated, without sunken areolae, while the 

 sutures and peripodia are more or less depressed. Each coronal plate bears a 

 well-developed primary tubercle, and these diminish regularly from the ambitus 

 upward and downward. There is a faint indication of a vertical ridge connecting 

 these tubercles; this is much more evident in the ambulacra than in the inter- 

 ambulacra and is most noticeable abactinally. The secondary spines and 

 tubercles are not very numerous, but on cleaned plates the tubercles are very 

 conspicuous. The plates of the abactinal system are distinctly swollen but 

 carry very few tubercles. The oculars are all broadlj' exsert. The periproct is 

 nearly 6 mm. across and is covered by numerous small rounded plates, among 

 which the suranal can scarcely be distinguished. The ambulacra arc 13 nun. 

 wide at the ambitus and the interambulacra, 22 mm. The pore-paii-s are large, 

 and the poriferous areas rather wide, becoming somewhat expandeii at the 

 peristome. The arcs of pores are quite oblique, and approach the horizontal 

 at the peristome. The gill-cuts are broad and shallow, almost wanting. The 

 buccal membrane is thick and carries only a few scattered plates distally. 



The smaller specimen is only 19 nun. in diameter and 10 nun. high, and is 



1 TvXos = a swelling or lump + eiSos = form. 



