192 HAWAIIAN AND OTHER PACIFIC ECHINI. 



ArseOSOma Owstoni Mortens. 



Araeosoma Owstoni Mortensen, 1904. Ann. Mag. Nat. Hist. (7) XIV, p. 82 ; Pis. II and 



V, figs. 4-9, 11, 18-20. 

 Asthenosoma Owstoni A. Agassiz and Clark, 1907. Bull. M. C. Z. LI, p. 117. 



Sagami Bay, Japan ; 50 fathoms. 



Plates 81, figs. 1, 2, 5, 6 ; 82, figs. 1-t. 



The specimens before us show considerable diversity of color, but it 

 is difficult to say how much of this is due to preservation. The small 

 individuals are very pale, almost white. Some medium-sized specimens are 

 decidedly reddish ; one is nearly brick red. The larger specimens are dull 

 pale purplish. In most of the specimens the actinal spines are decidedly 

 pinkish, while those of the abactinal side are greenish or not colored. The 

 pedicellariae agree with Mortensen's description and figures. Young speci- 

 mens of A. Oivstoni measuring 53 mm. and 21 mm. in diameter (Pis. 81, 

 figs. 1, 2, 5, 6; 82, figs. 1-4.) are characterized by the proportionally wider 

 ambulacral area as compared to the interambulacral one. In the specimen 

 measuring 53 mm. in diameter (PI. 81, fig. 2) the actinal primary inter- 

 ambulacral spines already carry a hoof. In the smaller specimen all the 

 actinal primary spines are broken or missing. The hoofs are very numer- 

 ous and very large on the primary actinal interambulacral spines of large 

 specimens (150 mm. in diameter). 



In the younger specimen (21 mm.) the two principal vertical rows of 

 interambulacral primaries are largest near the apical system (PI. 81, fig. 5), 

 but in the older one (PI. 81, fig. l) they already have all the characters of 

 the larger and full-grown specimens, both on the actinal and abactinal side 

 of the test. In the specimen of 52 mm. the primary abactinal interam- 

 bulacral spines are proportionally more slender and longer than in larger 

 specimens (150 mm. in diameter) in which they are relatively stout. 



The actinal system of the 52 mm. specimen (PI. 82, fig. i) is covered with 

 four and five horizontal rows of ambulacral plates, and close to the inter- 

 ambulacra there are a few minute elliptical plates. The ambulacral plates 

 carry a small secondary at the extremity of each plate and occasionally a 

 small miliary. At this stage (PI. 81, fig. l) the genitals and oculars are of 

 nearly the same size, the genitals separating the oculars (PI. 82, fig. 2). The 

 oculars, as in the young of many other species of Araeosoma, extend outward 

 between the two upper plates of the adjoining interambulacral areas. The 



