ECHINOIDEA. I. 



it is now also known from the sea south of Iceland, it is to be supposed that its distribution will 

 prove to agree with that of the three other Echinothurids mentioned in the preceding, so that it 

 belongs to the rich fauna found on the large slopes towards the deep of the Atlantic. 



9. Tromikosoma Koehleri n. g., n. sp. 



PL XI Figs, 2, 13. PI. XII. Figs. 22, 31, 41. PI. XIV. Figs. 12, 16, 19, 21, 23, 25, 28, 30. 



Of this species we have only one very large specimen, i8o mm in diameter, from st. 36 (61 50' 

 N. Lat 56 21' W. Iy. 1435 fathoms, bottom temperature 2), the Davis Strait. Unfortunately it is very 

 badly preserved, so that the description cannot be complete, and no figure can be given of the whole 

 animal. So many characters may, however, be distinguished in the animal before us, that genus and 

 species can be recognised with certainty. With regard to the generic characters see above p. 64 65. 

 The structure of the test cannot be described completely, as the whole actinal side is torn; 



the abactinal side, on the other hand, is whole, 

 and permits an examination of the form of the 

 plates (Figs. 5 6). The ambulacral areas (Fig. 5) are 

 uncommonly broad, a little broader than the inter- 

 ambulacral areas. The primary ambulacral plates are 

 angularly bent, with their top turned towards the 

 ambitus; the outer half is a litte narrower than the 

 inner one. The secondary ambulacral plates are 



Fig. 5. 



Fig. 6. 



Piece of ambulacral and interambulacral area of Tromiko- 

 soma Koehleri (>/,). in the animal the boundaries between particularly well developed , especially the outer one 



the plates are white, the plates of a bluish gray. , . , .. r ., 



which reaches quite to the edge of the ambulacral 



area. Near the apical area the inner accessory ambulacral plate reaches quite to the median 

 line where it adjoins the point of the primary ambulacral plate from the opposite side. Thus the 

 primary ambulacral plates of the same side are here quite separated. The pores of the accessory plates 

 are situated near the boundary line between the plates, the pore of the primary ambulacral plate is 

 placed about under that of the inner accessory plate. Also the interambulacral plates are angularly 

 bent, but in a direction contrary to that of the ambulacral plates (Fig. 6). 



The primary spines are placed rather scattered and irregularly. On the actinal side, near the 

 ambitus, 35 large spines are found, ending in a large, white hoof (PI. XIV. Fig. 30); (this, I suppose, 

 applies to all of them, but they were all broken, and the hoofs torn off were at the bottom of the glass in 

 which the animal was kept) They are not placed in regular series, in the ambulacral areas only one is 

 found in each plate, in the interambulacral areas two in each plate. The areoles are rather large, but 

 widely separated, forming no horizontal series. The whole actinal side is otherwise rather closely set with 

 fine secondary spines. The peristome is closely set with shorter, somewhat club-shaped, in the lower part 

 skin-covered spines, which are at all events some of them provided with a little hoof in the point 

 narrower than the spine (PI. XIV. Fig. 28). The hoof, as is commonly the case, is of another structure 

 than the spine, being smooth, compact, while the spine (at all events in the lower part) is tubiform, 

 and provided with thorny ridges; the hoof is very distinctly limited, so that it looks like a little joint 

 on the end of the spine. (Also the hoof of the large spines is sharply limited from the other part of 



