214 MEDUSAE OF THE WORLD. 



nii;ri<:ans. It is probable that Dipleurosorna brooksn is derived from a Staurodiscus 

 ancestor by tbe new formation of 4 interradial canals and the growing outward of the side 

 branches of the perradial canals until they join the ring-canal. 



Staurodiscus tetrastaurus Haeckel. 

 Plate 22, figs. 7 and 8; plate 25, fig. 5; plate 26, figs. 10 and 11. 



SlaaroJiscui tetraslaurus, HAECKF.L, 1879, Syst. der Medusen, p. 145, taf. 9, fign. 1-3. MAYER, 1900, Bull. Mus. Comp. Zool. 



at Harvard College, vol. 37, p. 46, plates 1 8, 19, figs. 47-49. MAAS, 1904, Sitzungsber. math . -phys. Klasse kg). Bayer. Akad. 



der Wissenschaft., Bd. 34, p. 440. BROWNE, 1907, Annals and Mag. Nat. Hist., ser. 7, vol. 20, p. 475. 

 Ottarrftna gelalinosa (young medusa), MAYER, 1900, Bull. Mus. Comp. Zool. at Harvard College, vol. 37, p. 8, plate 6, figs. 



20, 2 1 . 



Bell 4.5 mm. in diameter, and about twice as wide as high. In adult medusae there are 8 

 long, flexible tentacles with hollow basal bulbs. Some specimens have 24, others 16 sensory- 

 clubs upon the bell-margin. 32 black entodermal ocelli, one at the base of each tentacle-bulb 

 and sensory-club. Velum is well developed. Only 4 radial-canals reach the circular vessel. 

 From the middle points of each of these canals there arises a pair of equally developed side 

 branches that end blindly. The gonads are upon these side branches and on the distal 

 part of each radial-canal. The manubrium bears 4 prominent lips. Entoderm green or yellow. 



In the youngest specimen observed, the bell was I mm. in diameter and about as high as 

 broad. There were 4 well-developed tentacles, 4 rudimentary tentacle-bulbs, and 8 marginal 

 clubs. The medusa is common on the surface at Tortugas, Florida, in July and August. 

 Haeckel found this species in the Canary Islands, at Lanzerote. I have seen hundreds of 

 specimens at Tortugas and the side branches of the 4 radial-canals appear never to extend 

 to the circular vessel. 



Staurodiscus heterosceles Haeckel. 



Staurodiscus heterosceles, HAF.CKEL, 1879, Syst. der Medusen, p. 146. 



This medusa resembles S. tetrastaurus Haeckel, excepting that the two side branches from 

 each of the 4 radial-canals do not arise opposite one another from the middle of the radial- 

 canals, but one branch is long and arises from the main canal near the stomach, while the other 

 side branch is short and arises from the main canal beyond the middle point near the bell- 

 margin. The long branches arise constantly from one, and the short branches from the 

 opposite sides of the main radial-canals as one glances around the bell. 



Bell hemispherical, 6 to 8 mm. wide. There are 8 to 3*, usually 1 6, long tentacles with 

 globular basal bulbs, and 40 to 80 marginal clubs between the tentacles. There is an ocellus 

 at the base of each tentacle-bulb and marginal club. 12 club-shaped gonads, one at the 

 outer end of each of the 4 main radial-canals, and one upon each side branch. Stomach, 

 gonads, and tentacle-bulbs yellowish-brown. Ocelli black. Canary Islands, January, 1867, 

 Haeckel. Development unknown. 



Genus PTYCHOGENA A. Agassiz, 1865. 



I'lwhogena, Ar.ASSiz, A., 1865, North Amer. Acal., p. 137. HAECKEL, 1879, Syst. der Medusen, p. 147; 1881, Report on Deep- 

 sea Medusa?, Challenger Report, Zool., vol. 4, part xn, p. 7. 



\ ri Ptychogena, MAAS, 1893, Ergeb. der Plankton Exped., Bd. u. K. c., p. 64. 



I'lytliogetia, LEVINSEN, 1893, Vid. Meddel. Nat. For. Kjbbenhavn, ser. 5, Bd. 4, p. 145. LINKO, A., 1904, Zool. Anzeiger, Bd. 

 28, p. 217. BROWNE, 1907, Annals and Mag. Nat. Hist. ser. 7, vol. 20, p. 473. BICELOW, 1909, Mem. Mus. Comp. 

 Zool. at Harvard College, vol. 37, p. 149. TORREY, 1909, University California Publications, Zool., vol. 6, p. 13. 



This genus was founded by A. Agassiz, 1865, for Ptychogena lactea, found in Massachu- 

 setts Bay. 



GENERIC CHARACTERS. 



Thaumantiadae with 4 radial-canals which in the mature medusa give rise to numerous, 

 short, blindly ending side branches. The gonads are situated upon the radial-canals in the 

 interspaces between the side branches, close to the suhumbrella. The stomach is a wide, 

 Hat pouch and the mouth is a simple cruciform slit. The tentacles have no ocelli, and differ 

 in this respect from those of I. nod icca. 



