1866.] JjifeiTlSH Hi?DE6iDS A.KJB MBDUSi;. 481 



Banks to be unusually luminous, flashing in many parts like 

 liglituing. He directed some of the water to be hauled up, in 

 which he discovered .... a large species of medusa, to which he 

 gave the name pellucens. The Medusa pellucens measures about 

 six inches across the crown or umbrella." 



This is clearly from the figure and description a Scyphomedusa. 

 Shaw (1812) has copied the figure given by Macartney. 



Lesson (1843) has not only given Thaumantias hemispJiarica as a 

 distinct species, but also Thaumantias lucida, Macartney. Amongst 

 the synonyms of the latter Lesson has placed Medusa sciniillans 

 {=Noctiluca sciniillans) and Medusa pellucens (=Bank8's Scypho- 

 niedusn), but in the description of the species he only gives 

 Macartney's description of Medusa lucida. Haeckel apparently 

 has copied from Lesson, without referring to the original papers, 

 as he has placed as synonyms under Thaumantias hemisphcerica 

 both Medusa sciniillans and Medusa pellucetis. 



Forbes (1848) next described Thaumantias hemisplicerica. It is 

 first, however, important to consider Forbes's views upon the 

 value of seuse-organs or marginal vesicles for the identification of 

 the species. 



Forbes, in 1841, gave the following advice on the identification 

 of species belonging to the genus Thaumantias : — 



" 1st. The number of tentacula (always a multiple of four). 

 2nd. The presence, absence, size, and colour of the eyes at 



their bases. 

 3rd. The colour of the cross-vessels and proboscis. 

 4th. The shape of the umbrella. 

 5th. The shapes of the clubs of the vessels. 

 6th. The form and lobation of the oral proboscis or peduncle. 



" I have mentioned these sources of character in what I conceive 

 to be the order of their respective importance, but all should if 

 possible be noted." 



I may here say that Forbes's statement that the tentacles are 

 always a multiple of four is not correct. The multiple system is 

 also adopted by Haeckel, and it leads to the assumption that 

 Medusre have a most wonderful symmetry. The statement holds 

 good up to thirty-two tentacles, but above that number the 

 tentacles, when carefully counted, show odd as well as even 

 numbers. I found, out of 47 mature specimens of Obelia ludfera, 

 only two specimens showing an equal number of tentacles in each of 

 the quadrants, and only nine specimens possessing a number that 

 could be equally divided by four. Twenty-six specimens have an 

 even number of tentacles, and 21 specimens an odd number. 



Forbes included in his genus Thaumantias several MedussB which 

 have since been transferred to other genera, viz. : — 



Tliaumantias pilosella {=:Euchilota pilosella). 



Thaumantias lucifera (^= Obelia lucifera). 



Tliaumantias melanops (^ = Tiaropsis multicirrata). 



All these have certain characteristic features by which they may 

 Pboo. Zool. Soo.— 1896, No. XXXI. 31 



