28 THE VOYAGE OF H.M.S. CHALLENGER. 



1. Pontaster tenuispinus, Diiben and Koren, sp. 



Astropecten tenuispinus, Diiben and Koren, 1846, Ofversigt af Skandinaviens Echinodermer : Kongl. 



Vctensk.-Akad. HandL, Ar 1844, p. 251, pi. viii figs. 20-22. 

 Archaster tenuispinus, Sars, 1861, Oversigt af Norges Echinodermer, Christiania, 1861, p. 38, pi. iii. 



figs. 5-7. 

 (All succeeding writers have followed one or the other of these determinations.) 



This species, as indicated above, was originally classed as an Astropecten, and after- 

 wards as an Archaster. I have already briefly pointed out on a preceding page in my 

 remarks on the genus Pontaster that the morphological characters of this form do not 

 accord with those of either of the types to which it has previously been referred. The 

 generic diagnosis will sufficiently indicate the great difference in structure of this form, 

 and will at the same time bear evidence to the laxity of definition which has of late years 

 been entertained with regard to the conception of the generic limits of Archaster. 



This characteristic North- Atlantic Asterid has been well and unmistakably described 

 by its discoverers Diiben and Koren, 1 and subsequently by M. Sars,- Liitken, 3 and 

 Danielssen and Koren, 4 each of whom has added successively to our knowledge of its 

 anatomy and form. It is therefore unnecessary in the present place to recapitulate the 

 diagnosis of the species. Unfortunately, the material at my disposal is not sufficient 

 to enable me to indicate with satisfaction to myself either the range of the minor 

 individual variations to which the type-form is subject, or the details of the characters of 

 the young phases. This deficiency may, however, be supplied to a certain extent from 

 other sources ; and to this end I will limit myself to the remark that the descriptions 

 given by Diiben and Koren, and Sars, apply to young examples of the species ; whilst 

 that of Liitken is founded on specimens of larger growth, if indeed they do not actually 

 belong to the variety indicated below. Of the probability of this being the case I have 

 a very strong suspicion. It may, furthermore, be observed that the type is perhaps the 

 strictly northern form, which is found on the Scandinavian and Greenland coasts ; and that 

 the variety frequents the more southern habitats, and is also perhaps the deep-water form. 



Localities. — "Lightning" Expedition : 



Station 6. 5 In the Faertie Channel. Lat. 60° 45' 0" N., long. 4° 49' 0" W. Depth 

 510 fathoms. Bottom temperature o- 5 C. 



" Porcupine " Expedition : 



Station 76.' In the Faeroe Channel. Lat. 60° 36' 0" N., long. 3° 58' 0" W. Depth 

 344 fathoms. Bottom temperature 1°"1 C. ; surface temperature 10° - 1 C. 



1 K. Svensk. Vetensk.-Akad. Handl., A r 1844 (1846), p. 251, pi. viii. figs. 20-22. 



2 Oversigt af Norges Echinodermer, Christiania, 1861, p. 38, pi. iii. figs. 5-7. 



3 Videnskab. Medd. naturh. Foren. i Ejiibenhavn, 1871, p. 240. 



4 Nyt Mag. f. Naturvidensk., Bd. xxiii. 3die Hefte, 1877, p. 59, pi. iii. fig. 8; Den Norske Nordhavs- 

 Expedition, 1876-1878, Zoologi. xi. Asteroidea, Christiania, 1884, p. 85. 



These occurrences are recorded in Sir Wyvillc Thomson's Depths of the Sea; but I have not seen' the 

 specimens. 



