MEDUSAE OF WOODS HOLE REGION. 53 



THE TRACHOMEDUS/E. 



Petasid.e. — Radial canals 4; manubrium without peduncle, mouth usually simple, occasionally 4 

 fimbriated lobes; gonads variously folded or undulating, suspended beneath radial canals. Tentacles 

 numerous, usually solid. Otocysts variously distributed between bases of tentacles. 



Traohynemid.f.. — Radial canals S; manubrium long, devoid of peduncle, with mouth four-Iobed. 

 Gonads 8, home beneath radial canals. Sensory organs, otocysts with central otolith. 



Aoi.aurid.e. — Radial canals 8, manubrium long, with short distal hell-shaped stomach, and gelat- 

 inous peduncle; mouth usually four-lobed, rarely simple. Gonads usually rather long and cylindrical, 

 borne on radial canals or manubrium. Tentacles always solid. Sensory organs usually free. 



GeryoniD/E. — Radial canals 4 or 6, manubrium long and pendulous, with terminal stomach; 

 peduncle gelatinous, radial canals extending usually the entire length. Gonads usually flat and leaf- 

 like, borne on the subumbrella beneath radial canals. Tentacles of three series: Primary, occurring 

 during young stage, perradially distributed, and solid; secondary, interradiallv disposed, also solid, 

 and usually disappearing by atrophy; tertiary, the final series, hollow and communicating with the 

 marginal canal. Sensory organs are otocysts, each with a central otolith. 



Family PETASID.£. 



A single genus under this family comes within this region — namely, Gonionemus, which was by 

 Ilacckel referred to the cannotid Leptomedu.se (cf. System der Medusen, p. 146). Later and more 

 detailed knowledge both of the structure and life history of Giniioiuiiius has clearly demonstrated its 

 trachynemid affinities. While it does not easily come within the current limitations of the Petasid*, 

 the genus seems most closely related here, and it appears upon the whole better to enlarge the scope 

 of the present family than to establish an additional one. 



O0NI0NEMUS A. Agassiz (1862). 

 Gonionemus murbachii Mayer. PI. VI, fig. 1." 



Uimiunt uiiin verti its A. Agassiz, North American Acalephee, 1865, p. 128; in Contributions Natural History United States, Vol. 



IV, 1862, p. 350. 

 Gonyru ma miens Haeckel, System der Medusen, 1879, p. 147. 



Qonioni inn* murbachii Mayer, Bulletin Brooklyn Institute Arts and Sciences, Vol. I, 1901, p. 5. 

 Qonionema murbachii, Yerkes, American Journal of Physiology, Vol. VII. 1902. p. 181. Perkins, Johns Hopkins University 



Circular, May, 1902. 



This species was first described by A. Agassi', in 1862, from the Pacific coast. In 1895aspecies was 

 found at Woods Hole and supposedly identified with the Pacific species by Murbach, but it has since 

 been classed as a distinct species by Mayer. 



Gordom ■mini murbcuMi may be characterized as follows: Bell somewhat "less than a hemisphere, 

 though in early life, and even in many specimens approaching maturity, it is almost if not quite hem- 

 ispherical. Manubrium rather short, seldom extending to the velum, quadrangular in shape, with 

 4 prominent and delicately frilled oral lobes. Radial canals 4, though many specimens are found with 

 5, 6, or even 2 and 3. (Cf. paper on Variation in Hydromedusse, by writer, Biol. Bull., Vol. II, 1902. ) 



Gonads extending under radial canals in undulating folds. Tentacles numerous, 50 to 80 or more 

 in fully developed specimens, and with prominent basal bulbs of brownish color delicately tinged with 

 bright green. Each tentacle with a prominent, suctorial pad near the tip, at which point the tentacle 

 often presents a sharp knee-like angle. Sensory bodies, or otocysts, each with a central otolith, vari- 

 ously distributed between the bases of the tentacles. 



Ontogeny. — The life history and development of this medusa has recently been worked out with 

 much care by H. F. Perkins, who has thus shown that there is a well-defined, though lowly organized 

 hydroid generation, from which presumably, the niedusa- are derived by asexual budding. 



Color. — Bell transparent, radial canals and gonads yellowish-brown, manubrium brownish. 



Distribution. — Chiefly in the vicinity of Woods Hole, Vineyard Haven, and adjacent waters. 



" The figure is faulty ill some respects, but a better substitute was not available. 



