1906.] ALGYOXAllIAKS FROM ZANZIBAR. 439 



The stalk has a plump smooth appearance, but there are 

 numerous small spicules in the cortical layer. The number of 

 pinnules on each side is 46, but of these five on one side and seven 

 on the other, situated at the top of the stalk, are rudimentary. 



The metarachidial sui^face shows a bare streak 3-4 mm. in 

 breadth, loosely overlapped by the pinnules in its middle region. 

 There is no visible zooid sti-eak, but the surface is not very well 

 preserved. The prorachidial surface is smooth, and seems more 

 deeply coloured than the rest ; it varies in breadth from 3*5- 

 10 mm. The rachis ends bluntly in a small bare area. In the 

 other specimen the axis is exposed ; it tapers rapidly to a fine 

 point, and is soft and coiled for the last 14 mm. 



The pinnules are somewhat reniform, with a narrow insertion. 

 Thus, on one of the largest pinnules the insertion-line is only 

 4*5 mm. in length, but the outer margin is at least double. 

 There seems to be some irregularity in the number of the supr 

 porting calcareous rays, but in some of the pinnules 4-6 are very 

 distinct and project for about 1"5 mm. The specimen seems to 

 have been somewhat battered, and no importance can be attached 

 to the absence of rays in many of the pinnules. 



The zooid-plate is basal and strongly developed. It extends in 

 some about halfway up the pinnule ; it is ridged and has an 

 undulatory upper margin. 



The polyps occur in three or four rows on each side of the margin 

 of the pinnule, occupying a zone about 1-75 mm. in breadth. 



The spicules of the cortical layer of the stalk consist of small 

 rods and irregularly-branched forms. The following measure- 

 ments in millims. were taken : — 



Rods:— 0-2 X 0-03. 



Branched forms :— 0-25 x 0-175 ; 0-3 x 0-175. 



Locality. Wasin Channel, 8 fathoms. 



Pteroeides pulchellum, sp. n. (Plate XXVII. figs. 1 k 2.) 



A beautiful finely-preserved colony, 37 mm. in total length 

 and 13 mm. in breadth. The stalk is 16 mm. in length and 

 2-5 mm. in average breadth. 



There are 15 (and 16) pinnules, of which 4 (and 5) at the 

 base are very small. Each j)innule is supported by four rays 

 of spicules, which may project about 2 mm. There are about 

 30 polyps arranged on the margin in a sinuous line, occasionally 

 with young forms a little way doAvn on either surface. The 

 contracted polyps are barrel-shaped, with distinct longitudinal 

 i-idges, and the densely-crowded calices seem to differ much as to 

 the depth of the indentation between them. A common height 

 of calyx is 1 mm. ; the expanded tentacles are 0-75 mm. in length 

 and their tips enclose a circle about 1 mm. in diameter. There 

 is a prominent oral cone and a circular mouth-aperture. 



In some polyps the tentacles are pure white ; in others they 

 are backed by a chocolate-brown colour with a hint of blue. 

 This colour is also seen in the calices and on the rachis, especially 

 on its upper region. 



