Medusae of the world . little distance above the upper nerve-ring, and their cores consist of entodermal cells which aredirectly continuous with the entoderm of the circular canal (see Maas, 1893, p. 58, taf. 6, fig. 5). Mitrocoma is distinguished from Tiaropsis by the absence of ocelli in the entoderm of thecircular canal. Also in Tiaropsis there are no cirri. Mitrocoma is a good connecting link between the Eucopidae and the Thaumantiada?, for itpossesses marginal cirri similar in structure to those of the Thaumantiadae, while the presence otlithocysts places it among the Eucopidae. Metschnik
Medusae of the world . little distance above the upper nerve-ring, and their cores consist of entodermal cells which aredirectly continuous with the entoderm of the circular canal (see Maas, 1893, p. 58, taf. 6, fig. 5). Mitrocoma is distinguished from Tiaropsis by the absence of ocelli in the entoderm of thecircular canal. Also in Tiaropsis there are no cirri. Mitrocoma is a good connecting link between the Eucopidae and the Thaumantiada?, for itpossesses marginal cirri similar in structure to those of the Thaumantiadae, while the presence otlithocysts places it among the Eucopidae. Metschnikoff, 1886, points out the close relationshipbetween the hydroids ot Laodicea and of Mitrocoma. It seems possible that the genus Halopsis of the ^Equoridae may have arisen from someform of Mitrocoma through the multiplication of the radial-canals. Metschnikoff, 1886, reared the larvae produced from the eggs ot Mitrocoma anna of theMediterranean and they developed into hydroids having the characters of Cuspidella Fig. 153.—Mitrocoma cirrata (Mitrocomium cirratum), after Haeckel, 154.—Mitrocoma cirrata, from life, by the author. Zoological Station, Naples, Lithocyst. R. One of the ectodermal pigment spots on bell-margin. 1907. Mitrocoma anna? Haeckel. Mitrocoma anna, Haeckel, 1864, Jena. Zeitsch. fur Naturwissen., Bd. I, p. 332; 1879, Syst. der Medusen, p. 189,taf. 10, —Metschnikoff, E., 1886, Embryol. Studien an Medusen, Wien, pp. 23 (egg), 37 (segmentation), 54 (formation ofentoderm), 75 (development of hydroid), 82 (polypites), taf. 3, fign. 20-33; taf. 4, fign. 1-16. Halopsis anna, Metschnikoff, E., 1870, Verhandl. Gesell. Freunde Naturwissen. Moskau, p. 355, taf. 4, fig. 7. ( ? ?) Halopsis cruciala, Agassiz, A., 1865, North Amer. Acal., p. 102, figs. 151, 152. Non Mitrocomium anna, von Lendenfeld, 1884, Proc. Linnean Soc. New South Wales, vol. 9, p. 606. Bell flatter than a hemisphere, 30 to 40 mm. wide, with thick gelatinous walls. 6
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