224 MKIH'S.K OF THK WORLD. 



reach the circular vessel. The radial-canals of older medusae may branch more profusely. 

 The subumhrella consists of two strongly contrasted regions: An upper opaque part, nearly 

 hemispherical, contains the arches formed by the gonad, which spans space between proximal 

 pairs of radial-canals and stomach in a system of groined arches. The lower half of the 

 subumhrella is transparent and without these arches. 



There are 16 long, hollow, contractile tentacles with tightly coiled tips. In the young 

 medusa, with only i" terminal radial-canals, these tentacles arise from margin at base of each 

 canal; but in older medusae, with 32 terminal branches of radial-canals, the hollow tentacles 

 are in the radii of dichotomy. In addition to the long, hollow tentacles, there are a number of 

 short, stiff, solid tentacles, which remind one of the solid tentacles of Geryonidae, and are 

 carried turned upward from bell-margin. These short, stiff tentacles are equal in number 

 to the terminal branches of radial-canals. 



There are no marginal sense-organs, clubs, or cirri. The manubnum is a truncated cone, 

 extending about two-thirds the distance from inner apex of bell-cavity to margin. 



The gonads and manubrium in old medusae are opaque white. The radial-canals, cir- 

 cular vessel, and axes of hollow tentacles in young medusae are colored by brownish to orange 

 pigment-granules. The bell, subumbrella, and tentacles are nearly colorless in old medusas. 



This interesting medusa was found by Professor Brooks at Nassau, Bimini, and Green 

 Turtle Key among the Bahama Islands, and was described by him in detail. 



Genus DIPLEUROSOMA Axel Boeck, 1866, sens, emend. 



Difleurosoma, AxFLBoECK, 1866, Forenings Vidensk. Meddelclser, Nos. 10, 1 1, pp. 131,136. HAECKEL, i879,Syst. der Medusen, 

 pp. 155, 636. AOASSIZ A. AND MAYER, 1902, Mem. Mas. Comp. Zool. at Harvard College, vol. 26, p. 148. BROWNE, 

 1898, Proc. Zool. Soc. London for 1897, p. 826; 1900, Proc. Royal Irish Acad., ser. 3, vol. 5, p. 715. 



Telracannota, MATER, 1900, Bull. Mus. Comp. Zool. at Harvard College, vol. 37, p. 46; 1904, Mem. Nat. Sci. Brooklyn Inst . 

 Mus., vol. i, p. 12. 



Tetracannota + Dipleurosoma, MAAS, 1904, Sitzungsber. math.-phys. Klasse kgl. Bayer. Akad. der Wissenschaften, Bd. 34, pp. 

 440, 441. 



Ametrangia, ALLMAN, 1873, Nature, vol. 9, p. 73. 



The type species is Dipleurosoma t \picnm Axel Boeck, 1866, from the coasts of Norway, 

 Newfoundland, and northern Atlantic generally. 



GENERIC CHARACTERS. 



Thaumantiadae with 3 or more main radial-canals, some or all of which branch irregularly 

 (not regularly and dichotomously) and connect with the circular vessel. Gonads are upon the 

 radial-canals adjacent to manubrium. Tentacles numerous, and marginal clubs, cirri, and 

 ocelli may be present. The hydroid appears to be CuspiJelln. 



The radial-canals vary greatly both in number and arrangement in /). t\t>icntn, and are 

 best described by Browne, 1900. This extreme variability has caused the species to he 

 described under various names, fudging from the irregular arrangement in the single specimen 

 of D. pacifica found by Agassiz and Mayer, near Tahiti, the canals may be equally variable. 

 In D. collapsa they appear to be more regular, mature specimens having 16 canals arranged in 

 4 groups of 4 canals each. 



Dipleurosoma typicum Axel Boeck. 



Dipleurosoma typitum, AXEL BOECK, 1866, Forenings Vidensk. Meddelelser, Nos. lo-II, p. 131, fign. 1-3; Ibid., D. stuvitzi, pp. 



136, 137, figs. 1-4. BROWNE, 1900, Proc. Royal Irish Acad., ser. 3, vol. 5, pp. 696, 715, plates 20, 21. MAAS, 1904, 



Sitzungsber. math.-phys. Klasse kgl. Baver. Akad. der Wissenschaft., Bd. 34, p. 441. 

 Ameirangia htmhpharica, ALLMAN, 1873, Nature, vol. 9, p. 73. 



Difleurosoma tyficum+amfliithectum+ irregulare, HAECKEL, 1879, Syst. der Medusen, pp. 155, 636, taf. 9, fig. 9. 

 Dipleurosoma hemisph:rrica,a\DDON, 1885, Proc. Roy. Irish Acad., ser. 2, vol. 4, p. 526. BROWNE, 1898, Proc. Zool. Soc. London, 



for 1897, p. 826, figs. 10-12. 



Bell usually flatter than a hemisphere and about 15 mm. wide. Marginal tentacles very 

 numerous, more than 100. Each tentacle has a bulbous base with an ocellus upon its inner 

 side. There appear to be no marginal clubs in D. tvpicum, but these occur in D. pacifica of the 

 tropical Pacific. Velum well developed. Stomach is flat and watch-glass-shaped, with an 

 irregular outline, and there are 4 lips. In 217 specimens studied bv Browne from Valencia 



