2 THE VOYAGE OF H.M.S. CHALLENGER. 



The genus Thamnostylus with the single species Thamnostylus dinema (PI. I.) is the 

 only deep-sea Anthomedusa which I found among the collections of the Challenger 

 expedition. It belongs to the family of the Margelidse, to the sub-family of the Tham- 

 nostomidse, and is the only dissonematous genus of this sub-family, with only two 

 developed opposite marginal tentacles (like Cubogaster among the Cytaeidse). 



The genus Thamnostylus is distinguished by the remarkable development of the oral 

 organs ; the long central oesophagus, which projects below far out of the central stomach, 

 and the four strong numerously branched oral styles which spring from its basis are 

 much larger in proportion to the rest of the body in Thamnostylus than in the other 

 Margelidse. In other respects Thamnostylus dinema appears at the first glance a very 

 abnormal and peculiarly formed Anthomedusa. Closer consideration and comparison with 

 other Craspedotse shows, however, that its structure is not special or peculiar to itself. 

 We rather find in it a peculiar combination of striking characters, which appear other- 

 wise combined in other Anthomedusa?. The Margelidse Limnorea triedra and Favonia 

 octonema described by Peron (1809) appear to come nearest to it (Peron, Tableau des 

 Meduses, No. 8, Annales du Museum d'Hist. Nat., torn. xiv. p. 329). Leseur has given 

 a very good figure of both (in pi. iii. of his Recueil des Planches inedites des Meduses, 

 figs. 3, 5), which clearly shows a near relation to Thamnostylus and Nemopsis. Here 

 the oesophagus also projects out of the umbrella cavity, and is surrounded by a bush of 

 blood red much-branched oral styles which spring from its basis. On the ground of 

 these figures (which have been copied by Blainville (1834) and Milne-Edwards (1849), 

 L. Agassiz has placed Limnorea and Favonia among the Rhizostomata. (Compare my 

 System der Medusen, 1879, p. 87, and also the figure of Nemopsis heteronema, 

 p. 93, taf. v. figs. 6-9). 



Thamnostylus dinema, Hseckel (PL I.). 



Thamnostylus dinema, Haeckel. 1879, System der Medusen, p. 85, No. 95. 



Umbrella hemispherical, twice as broad as high. Stomach quadrangularly pyramidal, 

 reaching almost to the plane of the velum. Genitalia four egg-shaped swellings in the 

 wall of the stomach ; oesophagus quadrangularly prismatic, twice as long as the stomach, 

 projecting far out of the umbrella cavity ; four oral styles a little shorter than the 

 oesophagus, springing from its basis, 6 to 8 times dichotomised ; two opposite long, 

 strong tentacles, several times longer than the breadth of the umbrella. Horizontal 

 diameter of the umbrella, 16 mm. ; vertical diameter, 8 mm. 



Habitat. — Antarctic Ocean, south from the Kerguelen Islands. Station 153. Lat. 

 65° 42' S., long. 79° 49' E. Depth, 120 fathoms. 



The form of the umbrella is almost hemispherical, half as high as its greatest breadth 

 somewhat above the umbrella margin. The gelatinous substance thick, gradually and 



