Fewkes.l 392 [Nov. 2, 



ficial fungoid growths of this color sometimes exist on fishes, at 

 the time when Seriola was captured I was ignorant of this fact, 

 the red color led me to doubt its fungoid affinities. A glance 

 at the supposed fungus through a small lens easily dispelled my 

 error and showed me that I had a new and unique case of a par- 

 asitic hydroid. It is to the peculiarities in structure of this ani- 

 mal and the medusa which was raised from it that I wish to call 

 the attention of the Society this evening. 



As the genus of hydroid which shows this curious mode of life 

 is new, it will be necessary to assign it a name and I suggest that 

 of Hydrichthys mirus as expressing one phase at least of the cu- 

 rious life which it leads. 1 



The majority of genera of Hydmmedusse have ordinarily two 

 stages of growth, one of which is called the hydroid and the other 

 the medusa stage. The latter is a medusa-form zooid of the for- 

 mer. Let us consider each of these stages in Hydrichthys. 



Hydroid. — The hydroid of Hydrichthys consists of sexual and 

 asexual individuals, both of which arise from a flat plate of branch- 

 ing tubes which is fastened to the sides of the body of the fish. 

 The sexual individuals may be called the gonosomes, the asexual 

 the filiform bodies. 



The gonosomes consist of a simple contractile, highly sensitive 

 axis, upon the sides of which are borne lateral branches with ter- 

 minal clusters resembling minute grape-like bodies. These grape- 

 like bodies are medusas in all stages of growth. The filiform in- 

 dividuals are simple, flask-shaped bodies, without tentacles, and 

 with terminal mouths. 2 



No circle of tentacles about a mouth opening was detected either 

 in the gonosomes or the jilijorm bodies. This is a significant loss, 

 since, with the exception of Protohydra, Microhydra, and the sec- 

 ondary zooids of certain Alcyonians, tentacles of some kind are 

 found near a mouth or in relation to the oral opening of most of 

 the fixed hydroids or polyps. 



Medusa. — The gonophore of Hydrichthys has a Sarsia-like bell 

 and manubrium, four radial tubes, four tentacles without append- 

 ages, as already elsewhere described by me. 3 



In the light of what we know of the affinities of the medusa of 



1 An accurate diagnosis with figures will be found in my paper " On Certain Medusae 

 from New England." Bull. Mus. Comp. Zool., xill, No. 7. 



2 Somewhat like spiral zooids in Perigonimus except this particular. 

 s Bull. Mus. Comp. Zool., xill, No. 7. 



