54 



Hl'LLKTIN <>F THK BUREAU OF FISHERIES. 



Gunionemus has afforded some extremely interesting ecological phenomena. Its most congenial 



habitat seems to be in small protected [ Is or p Is, such as the Eel Pond at Woods Hole, which 



has onlv a narrow connection with the harbor, and being surrounded by dwellings, receives garbage 

 and other wastes which must render its waters inure or less foul. Eel grass grows luxuriantly in the 

 shallower portions, and in this the medusa' seem to find favorable conditions for lodgment and at the 

 same time abundant food, such as small crustaceans, fish-fry, etc. Thousands of specimens are 

 taken annually from this pond for use in the laboratory and elsewhere, but without apparently dimin- 

 ishing the numbers. When taken elsewhere, as at Vineyard Haven, the conditions have been very 

 similar. The adaptation of the species to such a habitat has seemed to tit it for aquarium life, which 

 in turn has made possible a most remarkable and varied amount of experimental work on coelenterate 

 physiology, as the abundant literature of the past few years amply attests. 



Family TRACHYNEM !!).€. 



Radial canals 



simple; no blind centripetal canals: otocysts it". . 



. RhopaXoni ma 



RHOPALONEMA Gegenbaur (1856). 

 Rhopalonerna typicum (Maas). Text cut. 



lliiiinriii inn typicum Maas. Memoirs Museum Comparative Zoology, Vol. XXII, 1897, p, 22. 



Rhopnlimi ma typicum A. Agassi z & Mayer, Memoirs Museum t lomparative Zoology, Vol. XXVI p. 152. Baigitt, Biological 

 Bulletin, Vol. IV, 1902, p. 15. 



Bell hemispherical in general shape, with a low, rounded apical projection. Average size about it 

 mm. in broad diameter by about 6 mm. in height. Radial canals 8, with the slightly developed gonads 



borne about the mid-region of their subumbrellar course. Manubrium 

 urn -shaped and with slightly flaring oral margins. Velum well developed 

 and capable of extension outward, a condition often assumed normally. 

 Marginal tentacles were lacking on the specimens taken, though a fairly 

 regular series of basal fragments indicated about the usual number char- 

 acteristic of the species'.. Those of the region adjacent to the radial 

 canals seemed to have been of larger size than the others. No otocysts 

 were distinguishable on the specimens. In view of the solvent action 

 of strong formalin on these bodies in other cases it may not be unlikely 

 that a similar effect resulted in the present case, for this condition pre- 

 Rhopalonema typicum. vailed with almost all the specimens of the collection. Ontogeny entirely 



unknovt n. 

 Colors. — Bell quite transparent, but with an evident irridescence; manubrium dull white, as were 

 also the gonads in the preserved specimens. 



Distribution. — Eegion of Gulf Stream, fragments taken in the tow in Vineyard Sound. The occur- 

 rence of the species in this comparatively high Atlantic latitude may seem extraordinary, if not 

 improbable, but there do not seem to be sufficient grounds for considering the specimens as distinct 

 from the species here indicated. Maas has described R. typicum from the west coast of Mexico (cf. 

 Memoirs Museum Comparative Zoology, Vol. XXII), and Agassiz and Mayer have recently recorded 

 it from the tropical Pacific (cf. op. (it. , Vol. XXVI, No. 3). 



It should be noted that the specimens taken in Vineyard Sound were [ill more or less damaged, as 

 already indicated. More perfect specimens and in larger numbers may afford grounds for a different 

 conclusion from that here expressed. 



u 



