SEMAEOSTOME^ — CHRYSAORA, DACTYLOMETRA. 



583 



Umbrella 70 to 100 mm. wide, 25 to 30 mm. high. Exumbrella thickly besprinkled with 

 nematocyst-warts. 32 marginal lappets, all similar each to each and all nearly semicircular. 

 24 laterall)' compressed tentacles, all somewhat longer than bell-diameter. The 4 subgenital 

 ostia are round to oval. The septa between the 16 radial stomach-pouches are nearly straight, 

 but the ocular pouches are a little broader than the tentacular pouches at the annulus of the 

 marginal sense-organs. The 4 oral curtains are as broad as the bell-radius near the mouth 

 and are very long with finely frilled margins. In contraction they are coiled, screw-like; 

 and in this condition are about as long as bell-radius. They taper to blunt points and their 

 thick proximal parts are covered with nettle-warts. 



Umbrella light brown, tentacles and midrib ot mouth-arms darker brown. Common 

 in Monterey Bay, California, in summer. 



Genus DACTYLOMETRA L. Agassiz, 1862. 



Dtictylometra, Agassiz, L., 1862, Cont. Nat. Hist. U.S., vol. 4, p. 166. — Agassiz, A., 1865, North Amer.Acal., p. 48. — Haeckel, 

 1880, Sy&t. der Medusen, p. 517. — Kishinouye, 1892, Zoological Mag., Tokyo, vol. 4, p. 261. — Agassiz and Mayer, 

 1898, Bull. Mus. Comp. Zool. at Harvard College, vol. 32, p. I. — Vanhoffen, 1902, W'issen. Ergeb. dculsch. Tiefsee 

 Expedition, Dampfer Valdivia, Bd. 3, Lfg. I, p. 39; 1906, Nordisches Plankton, Nr. 11, p. 50. 



The type species is D. lactca L. Agassiz, of the West Indies and South American coast. 



GENERIC CHARACTERS. 



Pelagidae with 40 tentacles, 5 be- 

 tween each successive pair of sense- 

 organs, and with 48 marginal lappets. 



Fig. 367.— CArysaora melanaun, according to Brandt, after Vanhoffen, in Nordisches Plankton. 

 Fig. 368. — Chrysaora gilberii, after Kishinouye, in Zool. Anzeiger. 



There is reason to believe that certain medusae may become mature with 24 tentacles, 

 while others, possibly better fed individuals of the same species, may develop 40 tentacles 

 before becoming mature. Similarly Dact\lometra longicirra of Japan may develop 40 or 

 even 56 tentacles before becoming mature. The conditions characteristic of the genera 

 Chrysaora, Dactylometra, and Kuragea may therefore be transitional stages in the growth 

 of one and the same medusa. 



Dactylometra lactea L. Agassiz. 



Chrysaora lactea, Eschscholtz, 1829, Syst. der .Acal., p. 81, taf. 7, fig. 3. 



Dactylometra lactea, Agassiz, L., 1862, Cont. Nat. Hist. U. S., vol. 4, pp. 125, 126, 166.— Haeckei., 1880, .Syst. der Medusen, 

 p. 517.— Lendenfeld, R., von, 1884, Proc. Linn. Soc. New South Wales, vol. 9, p. 271.— .'\gassiz. A., and Mayer, 1898, 

 Bull. Mus. Comp. Zool. at Harvard College, vol. 32, p. 7, plates 12, 13 and fig. 10, plate 7. 



