PENNATULIDA DREDGED BY H.M.S. "TRITON." 135 



slight interval (fig. 19), while the ventral polyps are separated by the whole 

 width of the ventral surface of the rachis. 



The polyps are retractile, and the extremes of contraction and expansion 

 are represented in the two polyps of the upper pair in fig. 18. As the figure 

 shows" there is no calyx formed during retraction, and the tentacles appear to 

 contract to a less extent than the bodies of the polyps. As in the case of 

 Virgularia tuberculata, the fact that the majority of the polyps have died in an 

 expanded or half-expanded condition may be taken as evidence that contraction 

 is effected slowly. 



Each tentacle is supported on its outer or aboral surface by a strong rib of 

 calcareous spicules shown on a larger scale in fig. 20. These spicules are placed 

 for the most part obliquely, running upwards and outwards; they have an 

 average length of 0*13 mm. and diameter of 0*02 mm. They do not extend 

 into the pinnules. 



At intervals along the body walls of the polyps spicules are found similar to 

 those of the rachis, but rather smaller and less abundant. 



Concerning the reproductive organs I have no observations. According to 

 Koren and Danielssen, # these are normally situated in the body cavities of the 

 fully developed polyps in the genus Dubenia ; but a large polyp from the middle 

 of the colony, which I opened for the purpose, had no trace of reproductive 

 organs. 



The zooids are few in number, and very small and inconspicuous. They 

 occur (fig. 19, e) as small rounded swellings on the dorsal surface between the 

 pairs of polyps, and also on the sides of the rachis just above the polyps. 



The genus Dubenia was established by Koren and Danielssen in 1874,t and 

 was at first named Batea, but that name being already appropriated for a genus 

 of Crustacea, it was changed in 1877 to Dubenia. It includes those members 

 of the family Stylatulidce in which the polyps, though fused at their bases, do 

 not form distinct leaves, the fusion not extending above the calcareous fan- 

 shaped spicular plate. The validity of the genus has been questioned by 

 Verrill and by Richiardt, but is accepted by Kolliker in his Eeport on the 

 " Challenger " Pennatulida, and may be considered as established. 



The " Triton " specimen has all the characters of Dubenia abyssicola var. 

 smaragclina, as defined by Koren and Danielssen. ;{: This variety differs from 

 the typical D. abyssicola in its more slender form, in its pale colour, and in 

 having the polyps in groups of two instead of three or more. Koren and 

 Danielssen express a doubt as to whether it should not be considered a 

 distinct species rather than a mere variety, a doubt which I must share without 



* Op tit, p. 24. 



f Magazin for Naturvidenskaberne, 1874. 



| Koren and Danielssen, Fauna Uttoralis Norvegice, part iii. p 96, 1877. 

 VOL. XXXII. PART I. Z 



