80 ECHINOIDEA. I. 



In the triphyllous pedicellarise the cover-plate is rather little developed; the outer edge is finely ser- 

 rate (PI. XII. Fig. 31); upon the whole they show no great difference from the common form. On the 

 other hand the ophicephalons pedicellarise are very peculiar (PI. XIV. Figs. 19, 23, 25). The valves are 

 highly constricted in the middle, the outer part widens suddenly to the same breadth as below, so 

 that the blade is somewhat widened in a wing-shaped manner. The edge is thick and strongly ser- 

 rate; the middle part of the blade is deep and perforated, the wing-shaped widenings flat, without 

 holes. The arcs below the articular surface peculiar of the ophicephalous pedicellarice, are well devel- 

 oped. The neck is short *- contrary to the ophicephalous pedicellarise of the Bchinids -- and it 

 seems to contain only longitudinal muscles. The stalk is quite different from that of the other pedi- 

 cellarise: a wide tube with rather few, small holes, somewhat widened above, but not below, only are 

 the holes here placed more close together than in the other part of the stalk. The length of the head 

 is ca. O'5 mm , that of the stalk ca. 3 mm . They are only (?) found on the abactinal side. 



The colour is gray with a slight indication of violet; in the living animal the colour was about 

 the same as in the preserved one. The spines white. 



Besides the species here described, at least one more species of the family of Echinothurids is 

 found in the northern Atlantic; Agassiz in Blake-Echini (9) p. 35 mentions a specimen of ^Phormo- 

 soma uranus* from the Faroe Channel; and on the basis of this statement Bell (73) and Hoyle (202) 

 mention Phormosoma uranus among the Echinids occurring in the British seas. Also SI ad en (367. 

 p. 701) mentions Ph. uranus from the south west coast of Ireland, as he finds a specimen before him 

 agreeing with the figures and descriptions of Wyv. Thomson and Agassiz. According to what 

 has been stated above (p. 58) with regard to <.< Phormosoma^ uranus, it is impossible to know with 

 certainty, whether the specimens that Agassiz and Sladen have had, have really been tPhormosoma* 

 (Echinosomd) uranus and not Hygrosoma Petersii. As no specimen of these two species has been 

 obtained by the Ingolf-Expedition, I shall give no thorough description of them, but only refer to 

 what has been said above of these species. Otherwise it may be taken to be probable that both these 

 species and also the Arceosoma Belli hitherto only known from Barbados, are found in the northern 

 Atlantic on the slopes towards the deep, and belong to the wonderfully rich archibenthal fauna, 

 peculiar to the smaller depths along the European and American coasts and across the Atlantic, south 

 of Iceland. The three mentioned species are therefore included in the following table of the North- 

 atlautic Echinothurids. 



Table of the Eehinothurids occurring in the Northern Atlantic. 



i. The primary spines on the actinal side straight, inclosed 

 by a thick bag of skin; great difference between the 

 actinal and abactinal sides. The tube feet on the actinal 

 side in one series. Only tridentate and triphyllous pedi- 



cellariae, the former simply leaf-shaped Phormosoma placenta Wyv. Thomson. 



The primary spines on the actinal side curved, ending 

 in a larger or smaller hoof 2. 



