116 THE VOYAGE OF H.M.S. CHALLENGER. 



with one end broad, and armed with spiny prominences ; the other pointed. The axis 

 is horny and fibrous. 



This genus stands in near rektionship to Echinogorgia, Kolliker, but at once 

 shows a difference in the more fully developed polyps and their opercular coverings, 

 and further in the form of the spicules. 



1. Acamptogorgia arhuscula (Gray, MS.) (PI. XXIII. fig. 7 ; PI. XXVII. fig, 5). 



Menacella arhuscula, Gray, in lift. 



Under tlie title of Menacella arhuscula, Gray, the Natural History Department of 

 the British Museum possesses the dried branch of an Alcyonarian which agrees in every 

 detail ^^^th a species in the Challenger collection ; the label attached to a portion of 

 Dr. Gray's specimen, which had been communicated to one of us, is in Dr. Gray's 

 handwTiting ; still it is difficult to understand why he should have placed it under the 

 genus Menacella, as this genus was characterised by Gray himself as having " polyp 

 cells covered with spicules like the bark," and those of the " bark " were described as 

 " very slender fusiform spicules." Piidley also, who has investigated the type of 

 Menacella (Menacella reticularis), coufii-ms the statement that this genus has only 

 simple spindles. The present species therefore cannot remain under the genus 

 Menacella, and for it as a tj^pe the present genus has been established. 



The colony has an upright stem, branched in one plane, with long branches at 

 considerable intervals. The principal stem arises from a smooth expanded base to a 

 heiglit of 270 mm., it has a diameter at the base of 3 mm., gradually narrowing to one 

 of I'D mm. On both sides, at angles of 45° to 60°, larger and smaller branches, 

 almost opposite to one another, and at varying intervals, arise, which in part remain 

 simple and reach to lengths of 15 to 20 mm., and in part are developed to a length of 

 120 mm., and then, in a similar manner to the principal stem, give off branches until 

 these again develop branches of a fourth order. The larger branches have at the base 

 A thickness of 1 to 2 mm. ; the terminal branches one of 6 mm. The apices of the 

 branches seem a little thickened at theii- terminations, ha\'ing a diameter of 2 mm. 

 The cceuenchyma is rather thick and rough. The polyps stand in spirals of three or 

 four on the stem and branches, at intervals of 1 to 1-5 mm., but at the apices of the 

 branches they are more closely packed and theii' bases are contiguous. The young 

 polyps arise on the apices of the twigs. The shape of the polyps is cylindrical or bluntly 

 conical, tliev are fixed at right angles on the branches. The operculum forms a low 

 cone. The basal diameter of the pol5"ps is 1"5 mm. with a height of 0"8 to 1 mm. 

 The spicules of the coeneuchyma are bent, spiny, papilUform spindles, frequently -with 

 short foliar expansions from their convex portions; 0'2 mm. in length; O'l mm. in 

 thickness with the foliar expansions, or 0'3 mm. in length, and 0"! mm. broad. On the 



