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



Off Cebu; 100 fathoms. January 22, 1875. 



Station 204. November 2, 1874. Lat. 12° 43' N., long. 122° 10' E. ; 100 fathoms 

 and 115 fathoms; mud. 



Astropyga. 



Astropyga, Gray, 1825, Ann. Phil. 

 Astro'pyga pulvinata. 



Gidarites pulvinafa, Lamk., 1816, Anini. sans. Vert. 



Astropyga pulvinata, Agassiz, 1846, C. R. Ann. Sc. Nat., vol. vi. 



In a young specimen of this species measuring only 19 mm. in diameter, the small size 

 of the actinostome, 5*5 mm., is quite exceptional, as one of the principal features which 

 distinguishes the old specimens of Astropyga pulvinata from Astrop)yga radiata is the 

 projDortionally large actinostome ; the tubercles of the actinal surface are in this small 

 specimen of quite uniform size in both areas, near the actinostome the large primaries 

 appearing only near the ambitus. On the abactinal side the special features to be noticed 

 are the crowding of the small ambulacral tubercles in the upper part of the zone and 

 the existence of a very prominent vertical row of large primary interambulacral tubercles 

 flanking the poriferous zone and extending well towards the abactinal area. The bare 

 median interambulacral spaces extending from the abactinal area are well defined, and the 

 large bright violet spots existing on each coronal plate on the outer edge of this bare area 

 extend to the ambitus. The anal tube of this young specimen is, as in all young 

 Diadematidse, long, and rises prominently above the anal system. On compaxing this 

 small specimen with two smaller specimens of Astropyga radiata collected at the 

 Philippines by Dr Semper we can at once distinguish the young of the two species by 

 the different as23ect of the actinal sui'face, which in the young of Astrop>yga radiata is 

 somewhat convex without presenting the close uniform tuberculation of that of the young 

 of Astropyga pidvinata. In the specimen oi Astropyga radiata, measuring 15 mm. in 

 diameter, the actinal opening measured 6 mm. In the other, measuring 12 '5 mm., the 

 actinal opening was nearly 6 mm. or larger than in the young of Astropyga pidvinata, 

 measuring 19 mm. in diameter. The pentagonal outline already noticed in a small 

 specimen of Astropyga radiata, measuring 36 mm. in diameter, becomes more prominent 

 in the smaller specimens measuring 15 mm. and 12 '5 mm. in diameter. It is very evident 

 from the above that in both these species we have considerable variation in some of the 

 characters which have thus far been employed to distinguish the two species. 



Unfortunately the series of specimens at my command are not such that a comparison 

 can be made of corresponding stages of the two species 



Station 190. September 12, 1874. Lat. 8° 56' S., long. 136° 5' E; 49 fathoms; 

 bottom temperature, 23'9° C. ; mud. 



