GERYONIADiE. 



Genus VIII. Geryonia, Peron (1809). 



Umbrella hemispheric, margin furnished with tentacula in variable number, 

 usually few ; radiating vessels five ; ovaries four, phylliform, on the surface of the 

 sub-umbrella in the course of the vessels ; peduncle rather long, conico- cylindrical, 

 terminating in a small campanulate stomach, opening by four lips. 



Geryonia appendiculata, Forbes, 

 Plate V, Fig. 2. 



One of the most phosphorescent Medusa of the British seas is the graceful Httle animal 

 I have now to describe. The umbrella is smooth, transparent, and of a hemispherical shape, 

 sometimes nearly sub-globose, slightly elongating during the act of ascending, becoming 

 more spherical when descending. The margin is fringed by eight distant tentacula, four of 

 which are of a different structure from the other four ; the former being cylindrical, and 

 composed of similar tissue (fibrous cells) throughout, whilst the latter have an outer and inner 

 side of different composition, the fibrous cells being collected in bundles or masses at regular 

 intervals on the inner surface. Both orders of tentacles appear to be tubular. Those of the 

 first kind are highly contractile, and capable of great extension, traihng after the body to 

 twice or three times its length when the animal rises, becoming short and thick when it 

 sinks. The intermediate tuberculated tentacles have not an equal power of extension. At 

 i;he origin, and by the side of each of the more extensile tentacles, is a globular body within 

 a cavity (otohtic ?) produced linearly upwards to terminate in a vesicular body, also with 

 contents (a rudimentary ocellus ?). A similar, though smaller and less defined, structure is 

 seen at the bases of the intermediate tentacles. Opposite to each of the longer tentacles is a 

 simple gastric vessel joining a marginal one, and proceeding down the inner surface of the 

 rather conical and truncated sub-umbrella. Towards the summit of the sub-umbrella in the 

 course of the vessels are the bases of four leaf-shaped, cordate, reproductive glands (in the 

 instances examined, ovaries). Round the opening of the sub-umbrella is a rather broad, 

 shelf-like veil. From its centre depends a long conical peduncle, extending for half its length 

 below the orifice of the disk. Its base is thick, and it tapers rather gradually nearly to the 

 extremity, a httle above which there is a constriction, marking the commencement of the 

 broad campanulate stomach. The gastric vessels commence at this point, and run up the 

 peduncle. The oral orifice is four-lobed, but these lobes or lips change form considerably, 

 sometimes appearing acute, sometimes obtuse, and occasionally as if six-lobed. They are 

 bordered by a highly contractile tissue composed of fibrous cells. Indistinct bands of similar 



