1907.] OP THE THIRD TANGANYIKA EXPEDITION. 255 



stated ; much more frequently they are distinctly angular, and 

 mostly triangular in shape. 



Araohnoidia ray-lankesteri Moore. (Plate XIY. figs. 5 & 6.) 



In his book 'The Tanganyika Problem,' 1903, Mr. J. E. S. 

 Moore (10) mentions on p. 295 a gymnol?ematous Polyzoon found 

 by him on shells of Parcmielania dredged from about 20 fathoms 

 off the shore of the lake, to which he gave the above name, 

 considering it allied to the marine genus Arachnidiam. 



This interesting species has been found again by Dr. Cunnington, 

 also on shells dredged from 20 to 25 fathoms near Mshale. The 

 colonies form an encrusting network, consisting of ovoid or 

 irregular, membranous, brownish cells, with toothed edges, closely 

 adherent to the shell, and connected together by narrow, tubulai", 

 creeping stolons. The cells or zooecia are very flat and shallow, 

 and have at their upper end a tall erect tul3e from which the 

 l^olypides protrude. The lophophore is circular, without calyx, 

 and has 16 narrow tentacles. A septum can be seen at the origin 

 of each stolon. 



In retraction the polypide retreats down the erect tube into 

 tlie cell, invaginating in the process the anterior thin-walled part 

 of the tube, which is the tentacle-sheath or kamptoderm. All 

 that can be perceived within the shallow cell is a band of retractor 

 muscles, and a sac filled with granules, possibly the stomach. 



This species belongs to the group of Gymnolpemata which I 

 have called "Cruciform Stolonifera," ancVcertainly ajjpears closely 

 allied to the marine genus Arachnidmm. 



Its mode of growth appears to be as follows : — A narrow, 

 filiform, closely adhei-ent stolon, following all the irregularities 

 of the surface of the shell, expands to form an ovoid cell, the 

 edges of which are more or less toothed, the better to fit the 

 depressions and ridges of the shell- surface. At the upper end 

 of the cell an orifice is formed which elongates into an erect tube, 

 whilst behind the orifice the stolon, after forming a septum, 

 continues to grow to form another cell at some distance further 

 on. At an early stage of the formation of the cells, stolons can 

 be seen growing out laterally, one on each side, rarely more, to 

 form side branches, and thus a very irregular cruciform network 

 is formed. The cells are always well separated from each other 

 by a stolon, and when found agglomerated together, as in 

 Mr. Moore's rough sketch, it is the result of two or more colonies 

 having grown over and in between each other. 



Of the polypide the indifl:erent preservation does not allow me 

 to say more than that the loiohophore has 16 narrow tentacles. 



The size of the lai-gest cell seen is 792 /t (-g-L in.) ; width of 

 stolon 69 |U (3-yo^ in.) ; length of the tube when the animal is 

 protruded 970 /.i {^^ in.). 



Victorella symbiotica, sp. n. (Plate XV. figs. 7 & 8.) 



Specific Characters. — Zoaiium a narrow, tubular stolon M'ith 



18* 



