528 EDITH M. PRATT. 



are usually only found on the ventral and lateral mesenteries, and I believe have not been 

 observed hitherto on the dorsal mesenteries in any species of the Alcyonaria. 



Zoochlorellae are very numerous in the endoderm of the tentacles, and are present, but 

 less abundant, in the endoderm of the mesenteries and in the coelenteric cavity of the zooids. 



Canal Systems. The vessels of the superficial canal system are broad and fairly 

 numerous. The transverse vessels lie in the mesogloea about "07 mm. below the surface and 

 are about "1 mm. in diameter. Both endoderm and lumen of these canals are densely crowded 

 with zoochlorellae, which are also present but are not so numerous in the vessels near the 

 surface of the internal system, which is similar to that of other species. 



A study of the anatomy of this species reveals many interesting features, which may 

 be briefly summarised. The autozooids are very small and are less numerous than in many 

 other species. In certain respects they show unmistakable signs of degeneration: — (1) the 

 tentacles are very short, blunt, infle.xible, and are only very slightly pinnate ; (2) the ventral 

 and lateral mesenteries are very feebly marked, and (3) have no mesenterial filaments. On 

 the other hand the siphonogl}^h of the stomodaeum, the dorsal mesenteries and their filaments 

 are all strongly marked. The occurrence of ova on the dorsal mesenteries is also interesting, 

 but is probably an aberrant feature, as they have not to my knowledge been previously 

 observed on the dorsal mesenteries in any species of the Alcyonaria. 



The degenerate character of the food-capturing and digestive portions of the zooids is 

 doubtless correlated with the presence of vast numbers of zoochlorellae in the endoderm and 

 lumen of the superficial canals and in the endoderm of the zooids, for in no other species 

 are the zoochlorellae so numerous nor the degeneration of the zooids so marked. It is 

 possible that the absence of siphonozooids may also be correlated with the strongly marked 

 character of the ciliated portions of the autozooids. In the absence of ventral and lateral 

 mesenterial filaments, and of siphonozooids, and the presence of a well-marked superficial 

 canal system this species resembles the genus Xenia. 



14. Sclerophytmn durum sp. nov. (PI. XXXI. figs. 29 — 32). 



Four specimens were taken. Three of them have a cup-shaped capitulum with marginal 

 lappets ; one of these has a rhizome-like outgrowth from the stalk which serves for additional 

 fixation (fig. 30 rh). The fourth specimen (fig. 29) is the largest and probably the oldest, 

 for ova are present at an advanced stage of development. This specimen is not cup-shaped, 

 but is proportionately shorter and stouter than the others and has a much lobed capitulum, 

 so that the specific identity of the four specimens was not easy to recognise. Careful and 

 minute examination, however, shows the difference to be one of facies only, for the anatomy 

 of all the specimens proved to be identical. All the specimens are extremely hard and 

 brittle. Enormous spicules (fig. 31 sp) can be seen lying parallel to the surface through the 

 ectodermal tissues. 



One cup-shaped specimen creamy-white in colour (in spirit) was taken near Nilandu at 

 a depth of 24 fathoms. Two cup-shaped specimens, one of which has a double cup, dirty 

 yellow in colour (in spirit), were taken on the Mahlos Atoll in shallow water. The lobed 

 specimen of a pale brownish-grey colour in spirit was taken on Addu Atoll, also in shallow 

 water. The specimens vary from 30 to 50 mm. in height, their capitula from 27 to 45 mm. 

 in diameter. Two of the specimens have slender, and two have broad stalks, the stalk of 

 the lobed specimen being proportionately shorter and broader than that of the rest. 



