On a new Eagle-Ray from Muscat. 141 



Above all, however, Russian naturalists have good oppor- 

 tunity to make closer acquaintance with the phenomenon, 

 since in our territories in certain localities (e. g. on Lake' 

 Issykkul) it may be observed not as an exception, but rather 

 as the rule. 



The question as to the causes of the luminosity of the 

 midges appears to me to possess a high biological interest and 

 to be worth an exhaustive investigation, even for the reason 

 that, should my hypotheses be confirmed, this phenomenon 

 would constitute the second instance of bacterial-pathological 

 luminosily in animals. 



St. Petersburg, 

 March 1894. 



XV. — Bescri-ption of a neio Eagle-Ray from Muscat. 

 By G. A.' BOULENGER, F.R.S. 



Rhinoptera Jayalcari. 



Teeth in nine rows, those of the median row of the upper 

 jaw eight times as broad as long, and nearly twice as broad 

 as those next to them ; median teeth of the lower jaw six 

 times as broad as long and once and a half as broad as those 

 next to them. Disk once and three fourths as broad as long. 

 •Head as long as broad ; snout emarginate ; the width of the 

 mouth nearly equals its distance from the end of the snout. 

 Skin smooth. Tail two tilths of the total length. Blackish 

 above, whitish beneath. 



millirn. 



Total length 740 



Length of disk 450 



Width of disk 750 



Length of head 130 



Width of head 130 



Diameter of eye 15 



Width of mouth 85 



A single male specimen, a skin ; presented to the British 

 Museum by Surgeon-Major A. S. G. Jayakar. 



By its dentition this species stands nearest to the Atlantic 

 R. Jussieui^ Cuv. {brasiliensis, J. Miill.), which is only 

 known to me from the descriptions ; but it can be easily 

 distinguished by its short tail, the tail of R. Jussieui being 

 more than twice as long as the disk. 



