422 PROCEEDINGS OF THE ACADEMY OF [1888. 



in a comb decreases towards the end of the arm. The ambulac- 

 ral feet are in two rows, 80-90 feet in each ray. There are twelve 

 spines at each angle of the mouth forming a single web. The four 

 central spines are the longest, the first pair of spines on the outside 

 of these rather smaller, the next half the size of the last pair, and the 

 two outermost pairs very short. Two large well developed secondary 

 mouth-spines in each interradial angle. 



Greatest diameter of specimen from tip of one arm to tip of an 

 opposite arm 100 mm. ; proportion of radius of disk to radius of arm 

 as 1 to 2 : height of disk 35 mm. 



A single specimen ; color in alcohol, dull yellowish grey. 

 This species differs from Pter aster pulv ill us, Sars, to which it appears 

 to be closely allied, by its longer arms; the absence of large conical 

 papilltTe upon the supra-dorsal membrane ; its greater size, being 

 about half as large again; the relatively much greater number of am- 

 bulacral combs and actino-lateral spines, and the different size and 

 number of tlie spines of the ambulacral combs. It also appears to 

 be closely allied to PL semireticulatus, Sladen, but may be distin- 

 guished from it by the prominent central spinelets of the paxillaj, 

 which perforate the supra-dorsal membrane; the greater number 

 and difference in size of the spiracula ; the absence of any tendency 

 towards a quadruple arrangement of the ambulacral feet — the great- 

 er number of ambulacral and mouth spines, and in its greater size 

 being about oi times as large as Pt. semireticulatus. It differs al- 

 together from Pteraster aporus, described by Dr. H. Ludwig from 

 Behring Sea, — Pt. aporus having no oscular orifice. Pt. aporus ap- 

 pears to be the only species of Pteraster that has hitherto been de- 

 scribed from that region. 



Below, I give a list of the species of Pteraster that have been 

 described up to the ])resent time. 

 P. militaris, 0. F. Miiller. Zool. Dan. Prodr. p. 234; Muller and 



Troschel, System der Asteriden, })p. 44, 128, pi. VI, fig. 1 ; 



Sars, Oversigt af Norges Echinodermer, }). 48, Tab. iv, v, 



vi, fig. 1-13. 

 P. militaris, O. F. Miiller, var. prolata, Sladen. Trans, Roy. Soc. 



Ediub. xxxii, p 153. 

 P. puvillus, Sars. Oversigt af Norges Echinodermer, p. 62, Tab. vi, 



figs. 14-18, Tab. vii, viii, ix, figs. 1-6. 

 P. multipes, Sars. Vidensk. Selskabs. Forliaudlinger, 1865, p. 200; 



Fauna litloralis Norvegiae p. (55. Tab. viii, figs. 1-17. 



