248 



MEDUSAE OF THE WORLD. 



Obelia dubia Nutting = ? Obelia dichotoma Hincks. 



Obelia dubia, Nutting, 1901, Proc. Washington Acad. Sci., vol. 3, p. 174, plate 20, fig. 1. 



Obelia dubia. Nutting, from Alaska = O .dichotoma, Hincks, according to Hartlaub, 1905, Zoolog. Jahrbiichern, Suppl. 6, p. 580. 



Trophosome. — Colony attaining a height of about 20 mm. Stem sparingly branched; 

 main stem and larger branches sinuous or slightly geniculate, giving forth pedicels singly or 

 in opposite pairs at bends. Pedicels rather long and annulated throughout; stem, also, more 

 extensively annulated than in most species of the genus. Hydrothecae very large, deep, tubular, 

 with very shallow undulations around margin, from between which lines run down for a short 

 distance on surface of hydrothecx. 



Gonosome. — Unknown. 



Found at Orca^ Alaska (Harriman Exped.). 



This species bears some resemblance to O. bidentata Clark, found on the New England 

 coast, but differs in the nature of the hydrothecal teeth, which are mere sinuosities instead of 

 being mucronate with two denticles each, as in the latter species. 



Obelia striata Clarke. 

 Obelia striata, Clarke, 1907, Mem. Museum Comp. Zool. at Harvard College, vol. 35, p. 9, plates 6 and 7, 13 figs. 



Hydrocaulus arises from a creeping stolon. Stems simple, clustered, 8 to 10 annula- 

 tions at base. Main stems rarely branched. 12 to 16 rings immediately above the origin 

 of each pedicel, 5 to 8 at the base of each hydrotheca. Hydrothecae pedunculate, alternately 

 arranged, deeply campanulate, very hyaline, tapering to the base; a well-marked diaphragm 



and basal cavity. Margin with 14 to 16 teeth with well-devel- 

 oped crests projecting inward; the distal part deeply fluted, 

 giving a series of longitudinal striations that are about one- 

 third as long as the hydrotheca. 



The gonosomes occur both on the stolon and on the stems. 

 Sessile, nearly cylindrical, tapering to the base, strongly curved. 

 Terminal opening in the center of a diaphragm-like membrane. 

 Young medusa with perradial tentacles. Tropical Pacific, 

 N. lat. 3V> W. long. 117° 15.8'. Attached to living shells of 

 Pteropods. 



Obelia hyalina Clarke. 



Obelia hyalina, Clarke, 1879, Bull. Comp. Zool. at Harvard College, vol. e, No. 10, p. 

 241, piate 4, fig. 21. — Congdon, 1907, Proc. American Acad. Arts and Sci., 

 vol. 42, p. 468, figs. 7-9. 



Hydroid. — The stems of the hydroid arise from a creeping 

 stolon. They attain a height of about 12 mm. and are but 

 little branched. They are annulated at base and divided into 

 internodes of equal lengths, each one of which is annulated 

 at its proximal end and bears at its distal end a pedunculated 

 hydrotheca. The pedicels of the hydrothecae are annulated at 

 both distal and proximal ends, and occasionally annulated 

 throughout. Hydrothecae short, tapering toward base. Rim 

 entire. There is an intrathecal partition near base of polypite. 

 Branches often arise in the axils of the pedicels. These are 

 annulate at base and give rise to hydrothecae like those of main 

 stem. Reproductive calycles small, being about twice as long 

 as hydrothecae. They are borne on short stalks that are 

 annulated throughout and arise from the axils of the pedicels of 

 the hydrothecae. The calycle tapers toward base and is rounded off at distal end, where there is 

 a flaring terminal opening. Medusae are developed in the calycles. The hydroid is very hyaline. 

 This species was found 10 miles north of Zoblos Island by Clarke. 



The best figures of this form are those of Congdon, who obtained specimens in Bermuda, 

 where it grows upon sponges, algae, and large hydroids of the shallow waters. 



FlG. 129. — Obelia hyalina, after Cong- 

 don, in Proc. American 

 Acad., vol. 42. 



