ball's brittle-star. 35 



OPIIIUMD&. 0P1UURM. 



BALKS BRITTLE-STAR. 



Ophiocoma Ballli. Thompson. 



Ophiocoma Dallii, Thompson, Annals of Natural History, vol. V. (April, 1840), 

 p. 99. 



Specific Character. — Disk round or angular, covered with imbricated scales, 

 two diverging broadly wedge-shaped scales at the base of each ray. Upper ray- 

 scales fan-shaped ; lateral ray-plates, each bearing four spines, which are as long 

 or sometimes longer than the breadth of the ray. 



This pretty little species, one of the many contributions to 

 the fauna of our islands, for which we owe thanks to the 

 indefatigable researches of Mr. Ball, was dredged by that 

 gentleman several years ago in Dalkey Sound on the coast 

 of Dublin ; and was described and named after its disco- 

 verer by Mr. Thompson in the fifth volume of that valuable 

 periodica], the Annals of Natural History. Several spe- 

 cimens of the Ophiocoma Ballli were taken ; the disk of the 

 largest was two and a half lines broad, and the rays were 

 nearly four times as long as its breadth. The disk is rather 

 flat, round ; in some specimens pentangular. The whole 



of the upper surface is imbricated with smooth scales, 



d2 



