362 MEDUSAE OF THE WORLD. 



Genus PETASUS Haeckel, 1879, sens. ampl. 



Petasus + Dipetasus + P?Msata+ Petachnum, Haeckel, 1879, Syst. der Medusen, pp. 247, 248, 249, 250. 



GENERIC CHARACTERS. 



Petasida: with free, marginal sensory-clubs and with tentacles arising at equal intervals; 

 not grouped in clusters. 4 sac-like gonads on the 4 radial-canals. 4 lips. No peduncle. No 

 centripetal vessels. Tentacles without adhesive disks. 



Haeckel describes a number of small and apparently immature medusae under the genera 

 Petasus, Dipetasus, Petasata, and Petachnum. He is the only naturalist who has seen any of 

 these medusa. Their generic characters, as given by Haeckel, may be summarized as follows: 

 Petasus, with 4 free, interradial sensory-clubs and 4 tentacles; Dipetasus, with 4 free, inter- 

 radial sensory-clubs and 2 tentacles ; Petasata, with 8 free, adradial sensory-clubs and 8 ten- 

 tacles; Petachnum, with 8 free, adradial sensory-clubs and 12 or more tentacles. 



These genera appear to me to be too narrowly circumscribed to be of service in a general 

 classification. For example, no allowance is made for the possible discovery of medusa? with 

 8 lithocysts and 4 tentacles or with more than 8 lithocysts and any number of tentacles. More- 

 over, when we study Haeckel's descriptions of these medusae we see a gradual increase in size 

 from those called Petasus to those designated Petasata and Petachnum. It is well known that 

 gonads often begin to develop upon the radial-canals of Trachymedusae at very early stages, 

 and one may readily be deceived into forming the opinion that such growth-stages are mature, 

 Haeckel distinguishes these forms as shown on page 361. 



Genus AGLAUROPSIS F. Miiller, 1865. 



Aglauropsis, Muller, 1865, Archiv. fur Mikroscop. Anatomie, Bd. 1, p. 144— Haeckel, 1879, Syst. der Medusen, p. 250.— 

 Browne, 1904, Fauna and Geog. Maldive and Laccadive Archipelagoes, vol. 2, p. 736. 



The type species is Aglauropsis agassizii F. Miiller, from the coast of Brazil. 



GENERIC CHARACTERS. 



Petasida: with small vesicular lithocysts upon the bell-margin between the tentacles. 

 Without free marginal lithocyst-clubs. Tentacles arise at equal intervals and are not grouped 

 in clusters. 4 gonads on the 4 radial-canals. 4 lips. No peduncle. No centripetal canals. 

 Tentacles without adhesive disks. 



This genus is closely related to Petasus, but it is distinguished by its inclosed vesicular 

 lithocyst-capsules and by the absence of free sensory-clubs upon the bell-margin. It is dis- 

 tinguished from Marotias by the absence of blindly ending centripetal canals. 



The species are very imperfectly known, Muller's description of the Brazilian and Browne's 

 account of" the Falkland Island medusae being incomplete. 



Aglauropsis agassizii Miiller. 



Aglauropsis agassizii, Mi-i.ler, 1865, Archiv. Kir Mikroscop. Anatomie, Bd. I, p. 144, taf. 7, fig. 4.— Haeckel, 1879, Syst. der 

 Medusen, p. 250. 



Muller's description of this medusa is so meager that even generic characters are not prop- 

 erly described. We only know that the medusa is found on the coast of Brazil and that it has 4 

 gonads on the 4 radial-canals and a large number of vesicular lithocysts and tentacles. The 

 medusa may be identical with Browne's Aglauropsis conantii. I can not separate this medusa 

 from Craspedacusta, yet our knowledge of it is so inadequate that I may not venture to unite 



the genera. 



Aglauropsis conantii Browne. 



Aglauropsis conantii, BuowME, 1902, Annals and Mag. Nat. Hist., ser. 7, vol. 9, p. 283; 1905, Report Pearl Oyster Fisheries, Gulf 

 of Manaar, p. 151. 



Umbrella bowl-shaped, with an everted margin, a little broader than high; 18 mm. high 

 and 20 mm. wide. About 200 or more marginal tentacles closely packed in two or three alter- 

 nating rows around the margin. About 50 or more internal lithocysts adjoining the ring- 



