323 



3) a third tier of 192 (or more) small tentacles placed in groups of 

 six between adjacent secondary tentacles. These are the tertiary 

 tentacles. 



Tentacle Rivets (Mantelspangen), connecting the roots of the ten- 

 tacles with the marginal ring (Nesselring), are connected with all the 

 tentacles of each of the three horizons. 



Otocysts, placed along the line of insertion of the velum — about 

 80 — 100 in number: from 16 to 25 are placed between successive per- 

 radial tentacles arranged in groups of 2 or three between the successive 

 secondary tentacles. 



Velar centrifugal canals — are peculiar to this genus formed by 

 the elongated otocysts which pass into the velum and there end 

 blindly. They possibly correspond in character to the centripetal canals 

 found in other Trachomedusae in the disc, but on the other hand may 

 prove to be ectodermal and not endodermal in origin. 



Their presence constitutes the chief peculiarity of the genus 

 and may necessitate the formation of a distinct family or even a sub- 

 order for its reception. 



The above characters are derived from examination of adult male 

 specimens which were freely discharging ripe actively motile sperma- 

 tozoa. 



The sole character which I can give as specific over and above the 

 generic characteres summarized above is that of size. The diameter of 

 the disc does not exceed Ya of an inch. 



Locality. — The water Lily-tank in the gardens of the Botanical 

 Society, Regents Park, London. 



Very abundant during June 1880. Probably introduced from the 

 West Indies. 



To the above diagnosis I would add a few words concerning the 

 otocysts with the minute study of which I am now engaged. It is by 

 no means clear that they belong to the type which the H e r t w ig 's have 

 considered as characteristic of Trachomedusae and Narcomedusae ; it 

 appears highly probable that these enormously elongated otocysts are 

 not derived from the gastro-vascular canal system, but are ectoder- 

 mal cysts and that the otolithic cells are also not endodermal but ecto- 

 dermal. In structure, and also in development, so far as I have been 

 able to determine from the examination (as yet) of only fresh speci- 

 mens, the otocysts belong to the type occurring in Leptomedusae, 

 being peculiar only for their elongation and extension within the 

 velum. If this proves to be the case, the new form will form a link 

 between the Trachelinae and the Leptolinae. 

 June 15th, 1880. 



