ECHINOIDEA. I. 



75 



(Hoyle, op. cit). Thus it seems to belong more to the sublittoral fauna than to the archibenthal one. 

 It is certainly only found in places with positive bottom temperature. North of the ridge in the Den- 

 mark Strait and the one between Iceland and the Faroe Islands it is scarcely found --- still less in 

 the deep regions North of Iceland. 



8. Sperosoma Grimaldii Koehler. 



PI. IV. Figs. 3-5. PI. XI. Fig. 9. PI. XII. Fig. 1 6. PI. XIII. Figs. 12, 23. PI. XIV. Figs. 2, 4, 43, 6, II, 31, 33. 



Literature: R. Koehler: 228. 229, p. 16. PI. II, III etc. 



Of this species we have two fine specimens from the Ingolfx -Expedition, st. 83 (62 25' N. Lat 

 28 30' W. L. 912 fathoms. Bottom temperature 3. The ridge south west of Iceland), a large one of a 

 diameter of 150", and a small one of a diameter of 27. The large specimen is much bleached, and 

 shows the violet colour only in spots --it has already been observed by Koehler that this species 

 has a tendency to lose the colour in alcohol; the small specimen has kept the colour very 

 beautifully. 



The large specimen agrees, with regard to the actinal side, exactly with the description by 

 Koehler; the abactinal side, on the other hand, shows some deviations, so that I felt a doubt whether 

 it might not possibly be another species than the specimens Koehler has had. So I sent the original 

 drawing of PL IV. Fig. 3 to Prof. Koehler, and asked him to give me his opinion with regard to this 

 fact, calling his attention to the deviations from his description, found in this specimen. He has then 

 informed me that in spite of the difference in the form of the plates and the arrangement of the pores 

 on the abactinal side he thinks it to be the same species, and trusting to his authority I refer this 

 beautiful specimen to Sp. Grimaldii. 



The ambulacral areas (of the abactinal side) are not narrower than the interambulacral ones, 

 but even a little broader. Just above the ambitus the middle part of the ambulacral area is only 

 formed by the primary plates, the inner accessory ambulacral plate is quite small, placed about at the 

 middle of the primary plate; the outer one is large reaching quite to the edge of the area, and often 

 expanding so much, that the primary plate does not reach to the edge. A little way, ca. 5 6 plates, 

 above the ambitus, the inner accessory ambulacral plate increases rather abruptly so much in size, that 

 it reaches quite to the median line of the area, and so it continues quite to the apical area. Thus the 

 primary ambulacral plates are here separated for their whole length; they are of almost the same 

 height from the median line of the area to its edge, and so the whole area looks rather regular 1 ). - 

 The tube foot belonging to the inner accessory ambulacral plate, is well developed, that of the outer 

 accessory plate and of the primary one is quite rudimentary. The two tube feet of the accessory plates 

 are placed quite near each other, just at the boundary line between the plates, and in about the same 

 height; that of the primary plate is placed opposite to the interspace between the two others. The 

 form of the interambulacral plates is also somewhat different from that in the figure of Koehler; they 

 are distinctly bent in an angular manner, with the point turned towards the apical area. 



The plates of the apical area cannot be seen through the skin, only the madreporite; the 



!) The figure (PI. IV. Fig. 3) does not render all these details of the structure of the ambulacral areas quite clear nor 

 quite exactly, but on the other hand it renders the habitus of the animal quite excellently. 



