80 



and Odontasteridœ and in Goniodon dilatatus. Doubtless they 

 will be found yet in some other Asterids, though in most of 

 the families they are certainly not found. It may be remem- 

 bered that neither in the Gidarids sphæridiæ are found. In 

 Chætaster longipes the spinules on the adambulacral plates and 

 the abactinal skeleton are of a homogenous, glassy structure 

 in their outer part, especially those of the adambulacral plates 

 looking very much like sphæridiæ ^). Whether they are also to be re- 

 garded as true sphæridiæ 1 dare not say, but Ï should think so, 

 though it seems a very curious thought that the whole animal 

 should be covered with sphæridiæ. — Also these spines ought 

 to be examined as to their histological structure. 



In the Pterasteridæ sphæridiæ are commonly occurring, 

 but not in all species. Thus in Pteraster obscurus the secon- 

 dary mouthspines are almost not transformed at all. Neither 

 in Hymenaster pellucidus , ?,\\q\\ a structure is found, if indeed 

 in any Hymenaster at all. 



14. Hymenaster pellucidus. Wyv. Thomson. 



Danielssen <feKoren: Op. cit. p. 72. — S laden: Report on the 

 Asteroidea of H. M. S. «Challenger». Vol. XXX. 1889. p. 508. — Ludwig : 

 Op. cit. p. 472. 



Forsblad Fjord, 90 — 50 fathoms, 2 specimens. — SE. off 

 Sabine Island, llOfath., 1 sp. 



The latter specimen differs very strikingly from the two 

 others and from the common form of H. pellucidus in having 

 three adambulacral spines, whereas this species otherwise has 

 only two adambulacral spines. The number of these spines is 

 of great systematic importance in this genus; S lad en (op. cit. 

 p. 494) even groups the species after their having one, two, 

 three or more adambulacral spines. It is then very remarkable 



') Ludwig: Die Seesterne des Mittelmeeres. Flora u. Fauna des Golfes 

 von Neapel. XXIV. Monogr. 1897. (p. 144. T. IX. Fig. 15 — 23). 



