390 MEDUSA OF THE WORLD. 



to their insertions in all specimens which have been studied. 64 lithocysts alternate with the 64 

 tentacles. Velum very large and powerful, being 3 mm. wide in a medusa 14 mm. in diameter. 

 8 straight, narrow radial-canals and a simple circular vessel. Manubrium octagonal at base, 

 4-sided below, the mouth having 4 simple, recurved lips is two-thirds to three-fourths as long 

 as the bell-height and lacks a peduncle. The gonads are said to be irregularly and diffusely 

 developed along the entire subumbrella edges of the 8 radial-canals. They begin to develop 

 when the medusa is about 12 mm. wide, and 9 mm. high (Maas, 1905, p. 56). 



In mature medusae the entoderm of the stomach and subumbrella lamella are of a beau- 

 tiful red color and the velum is white. In young medusae the stomach alone is red. 



Found at depths of 1,000 fathoms to surface in the tropical parts of the Atlantic, Indian, 

 and Pacific oceans. 



Vanhoffen, 1902, presents beautiful figures of this medusa, and Maas, 1905, gives a table 

 of measurements, together with a good figure. 



This may prove to be identical with P. haeckelii of the Arctic Ocean. Its only distinctive 

 character appears to be its bright red color, but the color of P. haeckelii is unknown. 



Genus HALICREAS Fewkes, 1882. 



Halicrras, Fewkes, 1882, Bull. Mus. Comp. Zool. at Harvard College vol. 9, No. 8, p. 306. — Maas, 1905, Craspedoten 

 Medusen der Siboga Expedition, Monog. 10, p. 56; 1906, Fauna Arctica, Bd. 4, Lfg. 3, p. 493, Jena. — Browne, 

 1908, Trans. Roy. Soc. Edinburgh, vol. 46, p. 237. — Bigelow, H. B., 1909, Mem. Mus. Comp. Zool. at Harvard College, 

 vol.37, p. 138. 



Halicreas+ Haliscera, Vanhoffen, 1902, Wissen. Ergeb. deutsch. Tiefsee Exped., Dampfer Valdivia, Bd. 3, Lfg. I, pp. 67, 68. 



Halicreas, Haliscera, Maas, 1904, Result. Camp. Sci. Prince de Monaco, fasc. 28, p. 21. 



Isonema (in part), Maas, 1906, Expedition Antarctique, S. Y. BeJgica, Medusen, p. 4, Anvers. 



Homaonema (in part), Bigelow, H. B., 1909, Mem. Mus. Comp. Zool. at Harvard College, vol. 37, p. 141. 



GENERIC CHARACTERS. 



Trachymedusae with a simple, conical stomach and round mouth-opening, without 4 lips. 

 No peduncle, 8 wide radial-canals upon which the 8 gonads are developed. Numerous ten- 

 tacles of various sizes arising in a single row from the bell-margin. Lithocyst-clubs between the 

 tentacles. No suckers upon the tentacles. Ring-canal simple, without centripetal diverticula. 



This genus is distinguished from Rhopalonema and Homceonema by its simple, round 

 mouth-opening without cruciform lips. Bigelow's, 1909, clear photographs show this round 

 mouth-opening. He also observed the tentacles in living medusae and finds that they are 

 arranged in a single, linear series and that each tentacle consists of a soft, flexible proximal, 

 and a stiff spine-like distal region. This remarkable condition is most characteristic of this 

 genus and serves at once to distinguish it. 



8 radially placed clusters of wart-like projections are often seen upon the sides of the 

 exumbrella above the margin, but these are not present in all species and are, according to 

 Vanhoffen and Maas, very variable in their development in any given species. A solid apical 

 projection may or may not be present and, according to Maas, 1905, its presence or absence is 

 not even of specific importance. Some specimens of H . papillosum have it well developed, 

 while from others it is absent. The 8 radial-canals are very broad, ribbon-like, and flat in all 

 known species. 



The oldest species is Haliaeas minimum Fewkes, of the Gulf Stream off the Atlantic 

 coast of America, but this is described from such imperfect specimens that it will be impossible 

 to determine it with certainty. It is probably identical with H. papillosum, Vanhoffen, 1902, 

 from the tropical Atlantic, Indian, and Pacific Oceans. The latter may, therefore, serve as the 

 type of the genus, for it will never be possible to determine Fewkes's specimens specifically. 



Vanhoffen studied an extensive series of specimens found by the Valdivia off the African 

 coast in the Atlantic and Indian Oceans. He separates them into two genera, retaining 

 Halicreas Fewkes, but instituting a new genus, " Heliscera," for medusae resembling Halureas 

 but with wider radial-canals, fewer tentacles, different color and a wider, more open mouth, 

 with a cylindrical, not conical, stomach. These distinctions are merely relative, and in my 

 system such intergrading characters are regarded as of specific, not of generic, value. Great con- 

 fusion invariably follows upon attempts to separate genera upon the extremes of intergrading 



