HYDROIDS OF BEAUFORT, NORTH CAROLINA. 



363 



Fig. 2j. — Obetia QCniculata 

 ( Linnaeus). 



Obelia hyalina Clarke. 



Obelia hyalina Clarke, Bull. Mus. Comp. Zool., Harvard. 1879, p. 241. 



Trophosome. — Colony small usually from 15 to 20 ram. in height; some colonies scarcely branched, 

 others of about the same height with several branches; stem distinctly geniculate with several annula- 

 tions above the origin of each branch and pedicel ; branches sometimes coming from the axil of a pedicel 

 and sometimes taking the place of pedicels; pedicels either short and annu- 

 lated throughout or longer and annulated at each extremity; hydrothecse cam- 

 panulatc, depth and width nearly equal; sometimes there is a tendency to 

 flaring of the margin; margin entire. 



Gonosome. — Gonophores borne in the axils of the pedicels; gonangia oval 

 but slightly tapering at the base; distal end either rounded or provided with 

 a distinct collar; length of the gonangium from two to four times the length of 

 tlie hydrotheca. 



Distribution. — Common on sargassum collected off Bogue Bank, but found 

 also growing on tunicates, growing on the piles at Marshallberg and on sponge 

 dredged by the Fish Hawk. 



Congdon found some specimens in the Bermudas which he considered to 

 be Obelia hyalina Clarke." Hargitt later found specimens on floating sargassum 

 at Woods Hole which he considered to be the same species as Congdon 's 

 specimens, but he did not agree with Congdon that it was O. hyalina. b He 

 called his species O. congdoni. Clarke says that in O. hyalina "the gonangia 

 are small, about twice the length of the hydrothecEc, rounded off at the distal 

 end, with a simple, spherical, terminal opening which stretches across the 

 distal end," and that the "colony is about 12 mm. in height and but little 

 branched," while in Hargitt's specimens "the gonangia ;ire large, about four times the length of the 

 hydrothecse, and the opening is not simple, but there is a terminal neck with an everted rim," while 

 "the colony is from 20 to 30 mm. in height and much branched." 



In the Beaufort material there were many colonies branched and many unbranchcd. Those that 



were branched had the branches coming out either at 

 the axil of the pedicel or taking the place of pedicels. 

 Gonangia with rounded distal ends were found in the 

 same colony as those with distinct collars. There was 

 much variation in size, and though I found few in my 

 own material bearing a ratio of 4 to i , as compared with 

 the length of the hydrothecae in the same colony , there 

 were plenty of them with an absolute measurement as 

 high as 7 mm., which is evidently as large as that fig- 

 ured by Congdon. This shows that the size of the ratio 

 is increased by the smaller size of the hydrothecae, 

 rather than by the larger size of the gonangia, as I 

 foimd to be the case in the few specimens w'here I 

 foimd the ratio as high as 4 to i. Moreover, in the 

 specimens obtained on the Bahama expedition by Prof. 

 Nutting and diagnosed by him as Obelia hyalina Clarke" 

 (in this diagnosis he had the use of Prof. Clarke's speci- 

 mens for comparison), the gonangia show a 4 to i ratio. 

 I did not find any colonies as much as 30 mm. high, but that is scarcely a criterion to base a dif- 

 ference of species upon, at any rate, in a branched form. Without being able to compare the speci- 

 mens visually it is impossible to say with certainty that the specimens all belong to the same species, 

 but from the facts above stated I can not think otherwise than that they do. 



Fig. 24. 



-Ohrlia Jiyatina Clarke. A. portion of colony; B_ 

 gonangia. 



o Hydroids of the Bermudas. 1907. p. 

 '> Biul. Bulletin. 1909. p. 375. 



c Narrative of the Bahama Expedition. 1S95. p. 89. fig. 3. 



