78 



ECHINOIDEA. I. 



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

 pro ve 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. 



■^i*?° 



Fig. 5- 



Fia;. 6. 



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



PI. 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, 180™" in diameter, from st. 36 (61' 50' 



N. Lat. 56° 21' W. L. 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 ns, that genus and 



species can be recognised with certaint)-. — 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 hånd, is whole, 



and permits an examination of the form of the 



piates (Figs. 5 — 6). The ambulacral areas (Fig. 5) are 



uncommonly broad, a little broader than the inter- 



ambulacral areas. The primary ambulacral piates are 



angularly bent, with their top turned towards the 



ambitus; the outer half is a litte narrower than the 



inner one. The secondar\' ambulacral piates are 

 Piece of ambulacral and luterambulacral area of Tromiko- 

 soma Koehleri {^li\. In the animal the boundaries between particularly well develojied, especially the outer one 



the piates are white, the piates of a bluish gray. , . , , •. , ,1 1 r .1 11 1 



■^ which reaches qnite 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 piates of the same side are here quite separated. The pores of the accessory piates 



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



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



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



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



ambitus, 3—5 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 uo 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 Hmited from the other part of 



