LEPTOMEDUS.E — MITROCOMA. 



289 



Mitrocoma cruciata. 



Halopsis cruciata, Agassiz, A., 1865, North Amer. Acal., p. 102, figs. 151, 152. 



Phialis cruciata, Haeckel, 1879, Syst. der Medusen, p. 181. — Hargitt, 1904, Bull. U. S. Bureau of Fisheries, p. 50. 



(r?) Mitrocoma anna, Haeckel, 1879, Syst. der Medusen, p. 189, taf. 10, figs. 1-13. 



Bell hemispherical, 40 to 50 mm. in diameter. About 100 slender tentacles with well- 

 developed basal bulbs, tentacles not over 25 mm. in length. There are numerous cirri between 

 the tentacles. There are 12 large lithocysts, 3 in each quadrant, each containing 5 or more 

 concretions. Velum well developed. There are 4 narrow, straight, radial tubes. Manubrium 

 very small, no peduncle. There are 4 recurved lips. The 4 gonads are developed upon the 

 outer halves of the 4 radial-canals. They are slightly sinuous, being somewhat longer than 

 the parts of the radial-canals upon which they are situated. Ova in female large and prom- 

 inent. The genital organs and bell are pink in color. This medusa was found at Nahant, 

 Massachusetts, in |une. It has not been seen since A. Agassiz studied it in 1862 and 1864. 



Mitrocoma megalota. 

 Halopsis nicgalotis, Maas, 1893, Ergeb. der Plankton Expedition, Bd. 2, K. c., p. 57, taf. 6, fign. 3-6. 



Bell flat, shield-shaped, with firm gelatinous substance, 40 mm. wide, 5 mm. high. About 

 100 very contractile tentacles. These are lash-like, tapering, with large, swollen, hollow, basal 

 bulbs, and only about one-eighth as long as bell-radius. About 800 very' short, solid cirri, 

 arising from bell-margin between the tentacles. 8 adradial lithocyst-pouches, similar in struc- 

 ture to those of M itrocoma anncc. These lithocysts are very elongate, open pouches, and lie 

 upon the subumbrella side of the margin at the base of the velum. Each pouch contains a 



Fig. 155. — Mitrocoma cruciata {Halopsis cruciata), after A. Agassiz, in North American Acalephae. 

 Fig. 156. — Mitrocoma megalota, after Maas, in Ergeb. Plankton Expedition. 



number of ectodermal concretions. There are no ocelli. Velum very narrow, its muscles weakly 

 developed. There are 4 narrow radial-canals and a simple, slender circular vessel. The 

 large stomach is quadratic at base, a radial-canal arising from each of the 4 corners. The 

 mouth is at the extremity of a short neck and is surrounded by 4 large, folded, crenated lips. 

 The gonads are swollen, linear, and lie upon the outer thirds of the 4 radial-canals. Each 

 gonad is developed upon both sides of its radial-canal, leaving the middle line of the canal 

 free. Found by the Plankton expedition off northwest coast of Scotland in July. 



Mitrocoma discoidea Torrey. 



Mitrocoma discoidea, Torrey, 1909, University of California Publications, Zool., vol. 6, p. 17, fig. 4. 



Bell flatter than a hemisphere, 45 mm. wide. 180 to 240 short tentacles with swollen 

 basal bulbs. 20 to 60 lithocysts with numerous concretions in 2 to 3 rows. Marginal cirri 



