012 SCHIZASTER FRAGILIS. 



Schizaster fragilis 



I Brissus fragilis Dun. o. Ivor., 1844, Skand. Echin., p. 280. 

 ! Schizaster fragilis A.GASS., 1847, C. It. Ann. Sc. Nat., VIII. p. 22. 

 (See Part II. p. 363.) 



PI. XXI. f. .;; PI. XXVI. f. &. 



Norway ; Gulf of St. Lawrence; Straits of Flori'la. 



Schizaster gibberulus 



! Schizaster gibberulus Agass., 1847. C. R, Ann. So. Nat., VTIT. p. 22. 



This seems to be a smaller species than S. canaliferas, judging from the 

 specimens preserved in collections. It is difficult for want of material to 

 make an accurate comparison of this species with the Mediterranean S. cana- 

 liferas, to which it is closely allied. It appears, however, to differ by its com- 

 paratively shorter lateral anterior ambulacra, the more anterior position of 

 the apical system, the usual presence of three or lour small genital openings, 

 the more flattened and elongate (posteriorly) test, the vertically truncated 

 posterior extremity, the proportionally coarser and more distanl tubercles, 

 and a deep re-entering angle of the fasciole in the lateral posterior interam- 

 bulacral spaces. 



Red Sea. 



Schizaster Philippii 



! Tripylus Philippii Gray, 1851, Ann Mag. X. II.. VII. p. 132. 

 Philippii A. Agass., 1872, Rev. Ech., Pi. I. p. 158. 



PI XXVI. f. 40- ;/• 



This species of Schizaster, which is closely allied to S. fragilis. and is its 

 Southern representative, has been referred by Gray to Tripylus, on the same 

 grounds which induced Sars to refer its northern congener to it. We 

 know now. however, that the number of the genital openings alone is 

 not a suitable generic distinction, and after Lutken's exhaustive comparison 

 and analysis of the reasons for uniting T fragilis to Schizaster, there is no 

 neces>ity for further discussion of the question of the generic affinity of these 



two species. 



Test depressed ; outline from above broadly elliptical, with deep anterior 

 indentation, made by the anterior ambulacra! groove. Apical system slightly 

 posterior, coincident with the vertex ; greatest breadth across that part of 

 the test. Anterior and posterior lateral petals slightly sunken ; anterior not 



