1915.] Fauna of the Chilka Lake : Coelenterates. 107 



possibility of its being the hydroid of a Phialidium is not, however, excluded, and it 

 may be the vegetative generation of the medusa described below as Phialidium cruci- 

 ferum. Of this there is no direct proof, but the fact that the medusae and hydroid were 

 found together in a fauna so poor as that of the Chilka Lake is at any rate noteworthy. 



The hydrothecae and the other purely vegetative parts of the colony agree well 

 with Bale's description and figures. The hydranth is much stouter in structure 

 (pi. ix, fig. 1) than that of Obelia spinulosa and has a wider and more trumpet-shaped 

 hypostome. The tentacles are less attenuated. The basal part of the hydrotheca 

 is separated off from the remainder by a delicate membrane. 



The gonothecae are mostly produced in groups and arise directly from the anasto- 

 mosing rhizome. They are placed vertically on very short, obscurely annulated stalks. 

 Sometimes they also arise on the stems, near the base of the stalks of the hydro- 

 thecae ; in this position their stalks are longer and more distinctly annulated. They 

 are somewhat variable in form, and often distinctly irregular and asymmetrical 

 in outline. Generally speaking, they may be described as being narrowly oval, ca. 

 4 times as long as broad and truncate distally, with a slight constriction near 

 the distal extremity and sometimes another about half way down. They vary in 

 length from o'68 mm. to 0-85 mm. There are no annuli on the surface. 



In the specimens of an Obelia from New Britain assigned by Miss Thornely L to 

 this species the hydrotheca was evidently much shorter than in Bale's types. 



Clytia serrulata was originally described (with Obelia spinulosa) from New South 

 Wales. We found a considerable number of specimens at two stations in the outer 

 part of the outer channel of the Chilka Lake in March, 1914, in salt water. The 

 species is probably a periodic immigrant into this part of the lake. 



The original Australian specimen was growing on another hydroid (Tubularia). 

 Ours were on a fragment of Pennaria that had been washed in from the sea, on roots 

 of grass, a dead leaf and dead Lamellibranch shells Many hydranths of those taken 

 at the mouth of the lake contain larval appendicularians in the gastric cavity and 

 these animals would seem to constitute an important element in the food of the 

 species. 



Genus Phialidium, Leuckart. 

 1910. Phialidium, Mayer, Medusae of the World II, p. 265. 



Although many medusae of this genus have been described none have been 

 associated with the hydroid in a satisfactory manner. Probably it is identical with 

 Clytia. 



Phialidium cruciferum, sp. nov. 

 (Plate ix, figs. 2, 2a, 2b.) 



As I have pointed out above, this may be the medusa of Clytia serrulata (Bale). 

 Our specimens met with an unfortunate accident, owing to which they are all some- 



1 Obelia serrulata, Thornely, "The Hydroid Zoophytes", etc., in Willey's Zoological Results, 

 p. 453, pi. xliv, fig. 5. 



