COMPARATIVE ANATOMY OF SOME BRITISH ACTINI/E. 527 



Colour : column buff, paler at base, with numerous faint longitudinal 

 lines best marked near the base. 



Disk pale yellow in the centre, darker on the outer area, radii paler, 

 A cycle of twelve distinct, nearly circular white spots is situated at the 

 junction of the two-colour areas. 



Tentacles dark chocolate-brown or maliogan}^ paler towards the tips ; 

 the tentacles of outer cycles are paler than those of the inner, and have 

 the basal bar more prominent. Innermost tentacles more or less dusky, 

 but always darker on their inner faces. There are three or four white 

 bars on this side ; Holdsworth calls them " rings," but if so they are 

 very indistinct on their outer faces. The apical bar is often very faint or 

 barely visible ; the basal bar, the third or fourth from the tip, is very 

 distinct. 



The following measurements were taken from a preserved specimen : — 

 Diameter of pedal disk=7 mm. 



,, ,, oral disk =3-5 mm. 

 Height of column =4 mm. 



Length of tentacles =2 mm. 



Arrangement of the mesenteries : This specimen shows an hexamerous 

 arrangement. There are four cycles, 6+6+12+24=4:8. The mesenteries 

 of the first two cycles are fully formed bearing reproductive organs 

 and mesenterial filaments. There are two pairs of directives and two oeso- 

 phageal grooves. The 4th cycle of mesenteries is only slightly developed. 



The column wall is not very strong, the mesogloea being less than half 

 the thickness of the ectoderm. The latter is a broad layer consisting of 

 tall columnar cells, which seem to get broader near the outer edge. This 

 ectoderm has an appearance quite different from that of S. miniata, where 

 it is more spongy and the cells are neither so regularly arranged nor 

 of such a uniform size as those of S. ornata. Gland cells seem to be 

 absent in the ectoderm of the column wall. 



The mesogloea is not very dense and a fibrous structure is distinctly 

 visible ; the fibres are very fine and form a close network, which becomes 

 denser near the endoderm. The mesogloea is not of uniform thickness, 

 because the ectoderm is raised into folds and these are supported by 

 processes of mesogloea, at any rate in a state of contraction. In 

 transverse sections near the summit of the column I have found a few 

 cinclides, but I have not found them present between two septa of a 

 pair, as Carlgren found in S. undata. The structure of these openings 

 is the same as that described for S. viduata and S. miniata ; they are 

 ectodermal invaginations. 



