556 



DR J. STUART THOMSON ON 



Japan. Kukenthal gives as the most important difference between Nidalia and 

 Metalcyonium, that in the former the gastral cavities of the polyps are in direct 

 connection with one another by means of transverse canals, while in the latter 

 communication is only indirect through an endodermal network. The latter fact 

 appears to be true for those species of Metalcyonium which I have recorded, but I fail 

 to see that in all those species which he regards as Nidalia the contrary holds. 



Metalcyonium clavatum, Pfeffer. 



Plate I. fig. 7 ; PI. II. fig. 9 ; PI. III. figs. 17 and 19 ; PI. IV. figs. 35-37. 



This description is based on four well-preserved specimens, with the polyps in 

 varying states of expansion. Each specimen consists of a basal supporting trunk and 

 an approximately cylindrical polyp-bearing portion. The following dimensions were 

 noted : — 





Specimen A 

 (P.F. 10,881). 



Specimen B 

 (P.F. 10,948a). 



Specimen C 

 (P.F. 10,948a). 



Length of entire colony, 

 Length of trunk, ..... 

 Breadth of trunk, ..... 

 Length of polyp-bearing part of colony, . 

 Breadth of polyp-bearing part of colony, . 



46 mm. 

 17 „ 

 06-8 „ 

 29-0 „ 

 13-0 „ 



55 mm. 



28 



08-0 „ 

 28-7 „ 

 10-5 „ 



18 mm. 

 10 „ 

 05-0 „ 

 8-5 „ 



5-8 „ 



The trunk expands slightly at the base, and in some cases fixes itself around organic 

 objects such as polychset tubes. The consistency of the trunk is extremely soft, and 

 its surface is marked by longitudinal lines and sometimes by transverse wrinkles ; its 

 colour is rose, slightly paler than the ground-colour of the polyp-bearing portion. The 

 latter shows numerous polyps, mainly colourless, but they are provided with eight bands 

 of red-and-yellow spicules in the tentacular part, and a few encircling spicules at the 

 base of these. The polyps are arranged in longitudinal but not straight ridges, each 

 of the latter being bordered laterally by lines separating it slightly from the adjacent 

 one. The polyps were almost completely retracted within the calyx. 



Well-expanded polyps showed the following structure : — 



1. An upper part (the crown), consisting of the tentacles and containing the upper 

 portion of the stomodaeum. This part is slightly broader than the succeeding part. 

 It shows the usual eight pinnate tentacles and eight bands of spicules (mostly red 

 in colour) arranged en chevron. There are a few encircling spicules at the base of 

 these longitudinal bands. The number of pinnules in each tentacle ranges from about 

 eight to twelve. 



2. The median portion of the polyp, containing the greater portion of the stomoda3um. 

 This part has no spicules either internally or externally, 

 transverse lines. 



It has longitudinal and 



