1906.] ALCTONARIANS FROM ZANZIBAR. 427 



Locality. Zanzibar ; very common among Zostera at low spring- 

 tide. Previously recorded from Baui, an islet in Zanzibar 

 Harbour. 



LiTHOPHYTUM RAMOSUM Quoy et Gaimard. 



A well-presei-ved specimen of this species showed no trace 

 of any spicules even in the canal-walls. The colour of the 

 preserved specimen is yellow-grey. 



Previously recorded from Zanzibar and New Guinea. 



LiTHOPHYTUM THYRSOiDES (Kiikenthal)= Ammothea thyrsoides 

 Ehrenberg. 



Several fine specimens of this common species, all belonging to 

 what Kiikenthal calls the asparagus-like variety — that is to say, 

 with cylindrical stalks rising parallel to one another and united 

 by a common basis. The colour of the preserved specimens is 

 yellowish white, in life it was brownish. One of the distinctive 

 features of this species is that the polyps arise directly from the 

 ends "of the stalks. The polyps are from 2-3-5 mm. in length by 

 1-1 "2 mm. in breadth. 



The spicules of the stalks and polyps are very slender spindles 

 with few warts. The following measuiements were taken of 

 length and breadth in millims. : — («) polyp-spicules : O'OQxO'Ol, 

 0-12 X 0-012, 0-18x0-016, 0-2x0-017, 0-25x0-016, 0-28x0-016; 

 {b) stem-spicules: 0-12 x 0-016, 0-16 x 0-016,0-3 x 0-02, 0-35 x 0-02, 

 0-4x0-02. 



Locality. Zanzibar. Previously recorded from Tumbatu Is- 

 land, on the N.W. coast of Zanzibar, and from the Red Sea. 



LiTHOPHYTUM THYRSOIDES (Kiikenthal), var. durum, nov. 



From a flat spreading base a large number of almost hemi- 

 spherical lobes arise. Each lobe is closely coveied by the pi'O- 

 jecting calycine portions of the polyps. The colour of the colony 

 is pale orange. The coenenchyma has a gritty structure, with 

 fairly abundant spicules. The spicules of the coenenchyma are 

 long slender spindles, either straight or slightly curved, with 

 small spines ai-ianged irregularly or in whorls. Their length varies 

 from 0-1 5-0-4 mm., and their width from 0-02-0-03 mm. 



Locality. Zanzibar, among coral, low tide. 



LiTHOPHYTUM FLAVUM (May). 



The species Lithophytutn africanum, Tj. Jiahellum^ and L.flavwm 

 seem to form a close group connected by intermediate forms. 

 There are several specimens in the collection which closely approach 

 L. j^lavmn, but differ from it in being far from rigid and in having 

 few spines on the spicules. We see no reason to emphasise this 

 quantitative distinction, especially as the boundaries of the three 

 species referred to are somewhat elastic. Their common features 

 are that several cylindrical stalks spring from a common base, 

 that the polyps are borne on short twigs springing from the ends 



