806 MR. J. RITCHIE ON HYDROIDS [May 24, 



as in simple Campamilarian hydroids, regeneration is not content 

 with simply adding a portion to the old stalk, but a complete new 

 stalk is reproduced, springing from within the truncated end of 

 the old one. 

 Dimensions : — 



Stalk, length ..' 0-43-0-98 mm. 



„ diameter 0-06-0-08 mm. 



Stolon, diameter 0-10 mm. 



Hydranth, length 0-34:-0-36 mm. 



„ greatest breadth 0-11-0-21 mm. 



Cnidoblast threads, armed with barbs such as Kii-kpatrick has 

 figured, accompany several of the hydranths. The}' are remark- 

 able for their large size, the barbed portion being 6 y:i in diameter 

 from tip to tip of the bai-bs. 



Localities. Rare hydranths on Thyroscyphus vitiensis and on 

 Idia pristis from St. 1, east of Tavoy Island and Port Owen, 

 4 to 12 fathoms, sand and broken shells, and mud. A solitary 

 hydranth on Idia pristis and a few on Corydendrium sessile from 

 St. 35, between Warden Island, Howe Island, and Lyall Island, 

 15 to 20 fathoms, rock and sand. 



The species has been previously recorded only from Murray 

 Island, Torres Straits, 15 to 20fathoms (Kirkpatrick, 1890, p. 606); 

 and. in Indian seas, from Paumben, 1 to 3 fathoms (Jaderholm, 

 1903, p. 263). 



Family P E x n" A r i D ^. 



*Pennaria disticha Goldfuss, 1820. Yar. austealis Bale, 1884. 

 {=Pennaria cavolinii Ehienberg, 1832.) 



A few well preserved colonies, the largest 30 mm. high, 

 represent this species. The ramules from which the hych'anths 

 project increase considei-ably in diameter upwards from their 

 origin, where they bear three or four annulations, to the distal 

 end, which is smooth. The number of filiform tentacles varies 

 from nine to twelve, but there is much variation in the number 

 of the capitate tentacles. The numbers depend, to some extent, 

 upon the age of the hydranth, for the tentacles are fewest in 

 those hydranths which, springing from ramules, lie towai-ds the 

 distal end of a branch — that is, in the youngest hydranths ; for 

 gi'owth proceeds by the elongation of a branch, new polyps 

 coming into being next to the terminal polyp, which is the olde-st 

 and the largest on the branch. 



Pictet's careful comparative study of colonies of typical 

 P. cavolinii from Naples, and of typical F. australis from 

 Amboyna, makes clear that the latter form falls within the 

 range of variation observed in the former species. But so 

 definitely limited is the basal ringing of the ramules from 

 which the hydranths arise, and so great a difference is there 



• For synonj-my, see Bedot, 1901, p. -159. 



[8] 



