278 MEDUSAE OF THE WORLD. 



This medusa was abundant in Hampton Roads and Norfolk Harbor, Virginia, in 

 October and November, 1904. It is at once distinguished from Blackfordia manhattcnsis by 

 the dense-black entodermal pigment-granules adjacent to the lithocysts. 



Genus PSEUDOCLYTIA Mayer, 1900. 



Pseudoclytia, Mayer, 1900, Bull. Mus.Comp. Zool.at Harvard College, vol. 37, p. 53.— Browne, 1904, Fauna and Geog. Maldive, 

 etc., vol. 2, plate 3, p. 730. — Maas, 1906, Revue Suisse de Zool., tome 14, p. 94. 



This genus was founded by Mayer, 1900, for Pseudoclytia pent at a of the Tortugas, 

 Florida. 



GENERIC CHARACTERS. 



Eucopidae with 5 simple radial-canals, 72 apart. The manubrium lacks a peduncle and 

 is provided with 5 simple lips. 5 gonads upon the 5 radial-canals. Tentacles and lithocysts 

 numerous. No cirri. 



Browne, 1904, described a medusa from the Maldive Islands, Indian Ocean, which may 

 belong to this genus, but it appears to be unsymmetrical, whereas the Tortugas species is 

 normally pentamerous and radially symmetrical. 



Pseudoclytia is probably derived by mutation from some 4-rayed Clytia-like ancestor. 



Pseudoclytia pentata Mayer. 



Plate 35, figs. 4 to 6; plate 36, fig. 7. 



Pseudoclytia pentata, Mayer, 1900, Bull. Mus. Comp. Zool. at Harvard College, vol. 37, p. 53, plate 12, figs. 24-26 ; plate 15, figs. 

 35, 35a; plate 39, figs. 131, 132; i90i,Sci. Bulletin, Museum Brooklyn Institute Arts and Sci., vol. 1, p. 3, plates 1-2, 

 figs. 1-67 (variations of 1,000 specimens). — Davenport, i 901, Biometrika, Cambridge, vol. i, p. 255 (variations). — Browne, 

 1904, Fauna and Geog. Maldive and Laccadive Archipelagoes, vol. 2, part 3, p. 730. 



Adult medusa (plate 35, fig. 4). — Bell flatter than a hemisphere and 8 to 13 mm. in diam- 

 eter. 20 simple tentacles with well-developed basal bulbs; each tentacle a little less than half 

 as long as bell-height. Neither lateral nor marginal cirri. 20 lithocysts alternate in position 



with the 20 tentacles; each lithocyst 

 contains a single spherical concretion. 

 Velum well developed. There are 5 

 straight, narrow radial-canals, 72 apart. 

 The 5 short, oval gonads are situated 

 upon the radial-canals at points mid- 

 way between the manubrium and bell- 

 margin. In the female the ova are large 

 and prominent, and when immature are 

 A % ) ° seen to have a well-defined nucleus and 



■>,_.,. , n /;,„,, b n .■ 111 . nucleolus. Manubrium flask-shaped, c 



I'IG. 150. — A. Pseudoclytia pentata. B. Clytia folleata. . . r > -> 



simple recurved lips. 



The entoderm of the stomach, gonads, and tentacle-bulbs is usually slightly milky in 

 color with a few scattered cinnamon-colored granules. Occasionally an individual is met with 

 in which these cinnamon-colored granules are developed to such an extent that the medusa 

 is brick-red (plate 35, fig. 6). In most individuals, however, the colored granules are so faint 

 as to be almost imperceptible. In some specimens there is a more or less decided green spot 

 in the entoderm of each tentacle-bulb. 



This medusa was exceedingly abundant at Tortugas, Florida, from June to August, 

 1897 to 1904. In 1905 it was relatively rare, and only 3 specimens were seen throughout the 

 summers of 1906 and 1907 although extensive search was made daily with the tow-net, and 

 not a single specimen could be found in 1908. At times during July, 1898, these medusa? 

 were so abundant upon the surface that one could not dip up a bucketful of water without 

 capturing several specimens. In 1909 it again appeared in fair numbers. 



This is the only pentamerous Hydromedusa known, and it has apparently arisen as a self- 

 perpetuating sport, or mutation, from some species of Clytia or Ph'talidium. Indeed the 

 medusa bears a close superficial resemblance to Clytia folleata McCrady, which is also abun- 



