REPORT ON THE ALC YON ARIA. 173 



Melitodes dichotoma (Pallas) (PI. XL. figs. 4, 5). 



his didwtuma, Pallas, Elench. Zoopb., p. 229. 

 ,, „ Esper, Die Pflanzentbiere, p. 43 ; Fortsetzung., p. 6, Tab. vi., xi. figs. 4, 5. 



„ „ Lamarck, Mum. Mus. Hist. Nat., t. i. p. 415. 



Mopsea dichotoma, Kolliker, Icones Histiologicie, p. 142. 

 Non Mopsella dichotoma, Gray, Cat. Lithopbytes, p. 10 ; Proc. Zool. Soc. Lond., 1857, p. 284. 

 N'ee Mopsea dichotoma, Milne-Edwards (pars) Hist. Nat. des Coralliaires, p. 197. 



The colony is attached ; it is more or less fan-shaped in form though sometimes it 

 branches irregularly, assuming a bush-like shape. It is from 130 to 190 mm. in height, 

 but varies much in width and depth. The basal attachment is broad, reptant, sometimes 

 stoloniferous, and bearing polj'ps, from which apparently new vertical colonies arise. 



The branches show a tendency to originate in the one plane, but in some cases the 

 branches arise in an irregular manner ; the branches shortly after their origin divide 

 into twos, and this with a certain regularity. The anastomosis varies very much ; in some 

 specimens there is no anastomosis between the branches of a colony, but a feeble 

 anastomosis between the branches of a neighbouring colony. In others there is an 

 irregular anastomosis between some few of the branches, and this in even different planes, 

 but no true mesh system is formed, and the extremities of the branches are free for a 

 considerable distance below their terminal points. The main axis and branches, when 

 clothed with the pol>"ps and coenenchyma, are cylindrical, and show no distinction between 

 the nodes and internodes. The axis has an average basal diameter of 4 mm., diminishing 

 to one of 1"5 to 1 mm. for the twigs. 



When deprived of coenenchyma, the internodes are found to vary in length, being from 

 4 to G mm. in the basal portion of the colony, and from G to 8 mm. in the terminal 

 portions. The nodes are not prominent, being in fresh specimens of the same diameter 

 as the internodes, i.e., about 2 mm. towards the base and 0"5 mm. beneath the terminal 

 internodes. 



The polyps are crowded irregularly on the front and sides of the branches ; while 

 on the back of the colony, except at the extreme tips, they are absent, and here the 

 ccenenchyma is striately marked. The polyps are lodged in well-developed verrucse, 

 wliich measure about 1*25 mm. in diameter, and 1 mm. in height. The polyps are 

 retractile within the verrucae. 



The ccenenchyma is thick and dense, it has a layer of large, half-sided, spiny spindles, 

 the spines on the one side largely developed, and short four-rayed spicules. Other 

 spicules of the ccenenchyma present the forms of warty spindles (Stachelkcule of Kolliker), 

 or feebly developed blattkeule, four-rayed stellate forms (Vierling of Kolliker), spiny 

 one-sided spindles, bent spindles, and of warty double spindles. These spicules also 

 cover the verrucse. The polyp spindles are straight and bent spiny spindles. 



The spicules, which are of a light red colour, measure : — the half-sided spiny spindles 



