6 MUSEUM, BROOKLYN INSTITUTE OF ARTS AND SCIENCES. 



the more primitive and universal co-operation of both ectoderm and ento- 

 derm. 



New Species. Two new species were established, Lymnorea Alexandri, 

 named in honor of the author's constant friend, Alexander Agassiz. It is the 

 most abundant medusa of the Bahama Banks throughout the summer. 



The other new form has been named Parvanemus degeneratus, and is the 

 most degenerate free-swimming hydromedusa yet described. It lacks tenta- 

 cles, sense organs, and peripheral vascular system. It swims, however, with 

 great activity, but is short-lived. In this form nature appears to have per- 

 formed Loeb's experiment, in which, as is well known, he cut away the rim of 

 the bell, depriving the medusa of tentacles and sense organs. Yet the bell 

 still contracted rhythmically when placed in a solution having the same os- 

 motic pressure as sea water, but having no calcium or potassium ions. 



Murbach, 1903 ; Amer. Journ. Physiology, X, p. 201, has shown, however, 

 that in Gonionemus the marginal otocysts have nothing to do with the main- 

 tenance of equilibrium, but that it is probable "that muscular sensation 

 (largely in the velum) is the seat of static function in Gonionemus and in 

 hydromedusae." It is interesting to observe that the velum of Parvanemus is 

 exceptionally large and provided with powerful muscles. Such "muscular 

 sensation" is not always found in the velum, however, for in Ehacostoma dis- 

 par the bell opening is much reduced and the medusa is propelled by the 

 movements of its widely open mouth. Bull. Mus. Comp. Zool. at Harvard 

 Coll., Vol. XXXVII, p. 61, 1900. 



DESCRIPTION OF SPECIES. 



For the sake of completeness we present a brief description of all species 

 of Hydromedusae known from the Bahamas. 



The classification is essentially that of Haeckel. 



HYDROMEDUSAE. 



Parvanemus degeneratus, gen. et. sp, nov. 



Fig. 22, Plate III. 



Generic Characters: Parvanemus: Codonidae without tentacles, radial 

 canals, or circular vessel. 



