280 Verrlll, Notes on Radiata. 



Nidorellia, 



This name was applied by Dr. J. E, Gray* to a section of his genus 

 Pentaceros ( Oreaster M. and Tr.), which included only the following 

 species. Although the character of having movable spines, which 

 he attributed to it, seems not to exist, it has so many important dif- 

 ferences from typical Oreaster, in external form and structure, which 

 we must suppose to be connected with still more important internal 

 peculiarities, that it appears worthy of being separated as a distinct 

 genus. 



Until a comparative study of the internal structure shall have been 

 made we can only indicate some of the more important external pecu- 

 liarities for distinctive generic chai*acters. 



Such are the broad depressed disk, the short, broad, depressed rays, 

 rounded at the ends ; the elevated margin, with large plates, those at 

 the ends of the rays largest and swollen. 



Nidorellia armata Gray. 



Pei\taceros (Nidorellia) armatus Gray, Ann. and Mag. Nat. Hist., vol. vi, p. 276, 1840. 

 Oreaster arTnatus Mull, and Tr., System der Asteriden, p. 52, 1842. 

 Goniodiscus armatus Liitken, op. cit., 1859, p. 75 (p. 51 of pamphlet). 

 Oreaster armatus Lutken, op. cit., p. 148, 1864 ; E. vou Martens, Monatsb. Akad., 

 Berlin, 1865, and Ann. and Mag. Nat. Hist, xv, p. 433, 1865. 



ISTumerous specimens of this species were collected by Mr. Bradley 

 at Panama and the Pearl Islands, and Zorritos, Peru. It occurs on 

 the reefs at low-water. Prof. B. Silliman has, also, presented two speci- 

 mens from Panama. It is also found at Realejo and Puntarenas, — Dr. 

 Ltitken ; Punta Santa Elena, — Dr. Gray ; Gulf of Nicaragua, Costa 

 Rica, — Dr. E. von Martens. f 



Our largest specimen is 6*5 inches in diameter, the smaller radius 

 being 2-'75 and the greater 3 •25, 



The specimens vary greatly in the number and arrangement of the 

 large conical spines ; and in the spines of the marginal plates, which 

 may be numerous, both above and below, or entirely absent. The 

 pedicellarife are also very variable, sometimes beng entirely absent, 

 while other specimens have numerous large, two-lipped ones, near the 

 mouth or scattered on the lower surface, and smaller ones on the 

 lower marginal plates, or even on the upper ones. All these varia- 

 tions are too inconstant to allow the species to be divided into varie- 

 ties. Sometimes the extreme variations are found on the different 

 rays of the same specimen. The number of spines of the dorsal sur- 



* Annals and Magazine of Natural History, vol. vi, p. 275, 1840. 



•j- Capt. Pedersen has recently sent several large specimens from La Paz, — Reprint. 



