PENNATULIDA DREDGED BY H.M.S. "TRITON." 129 



should be greatly tempted to suppose that as one set of specimens — the typical 

 P. phosphorea — is obtained from a depth of only 40 fathoms, and the other, 

 the variety aculeata, from 555 fathoms, that the structural differences between 

 the two forms may be at any rate in part due to the different external condi- 

 tions of pressure, &c. 



Although, however, the variety aculeata does appear to occur as a rule 

 in deeper water than the more normal form, yet this rule is not universal, for, 

 as we have seen above/" Sars obtained specimens of aculeata off the Norwegian 

 coast at depths of 30 to 70 fathoms. The determining cause therefore that 

 leads to the production of the variety aculeata must be some other than mere 

 depth, though this would appear to have some influence. 



It may be noticed, finally, that the vertical range of P. phosphorea, which 

 KoLLiKERt puts at 30 to 300 fathoms, has been nearly doubled by the " Triton " 

 dredgings, which show that the species lives in abundance, though in a rather 

 diminutive form, as low as 555 fathoms. 



Sub-section 2. Virgulariece. 



Family 1. Virgularidae. 



Virgularia, Lam. 

 Virgularia tuberculata, n. sp. (PL XXI. figs. 1-3.) 



Specific Characters. — Polyps nearly sessile, united at bases in groups of 

 three, the groups alternating on the two sides of the rachis. Calyx completely 

 obliterated when the polyp is fully protruded ; calyx margin marked by eight 

 small tubercular processes placed opposite the tentacles. Reproductive organs 

 in the immature leaves at the lower part of the rachis. Stem cylindrical. Colour 

 of colony, yellowish-white. No calcareous spicules in any part. 



Habitat. — Station 11. 



Of this species three specimens were obtained, all of which are imperfect. 

 The largest specimen (PL XXI. fig. 1) measures 68 mm. in length, and consists 

 of the stalk and lower part of the rachis ; its upper end is abruptly truncated, 

 and the upper 10 mm. of the stem are denuded of the fleshy sarcosoma. 



The second specimen is similar to the first, but smaller in all its dimensions ; 

 it has a total length of 364 mm., and consists of the stalk and lower end of 

 rachis, the upper end of which is abruptly truncated. 



The third specimen is 46 mm. long, and consists of the middle portion of 



the rachis of an apparently rather larger specimen than either of the other two ; 



truncated at both ends. 



* Supra, p. 123. 



f Zool. Chall. Exp., part ii. p. 38, 1880. 



