1906.] ALCYONARIANS FROM ZANZIBAR. 413 



Xenia rigida, sp. n. 



A small colony 15 mm. in height by 12 in breadth, and 8 in 



thickness. • i • 1,4- 



The polyps are stifi" and snbstantial, about 3-5 mm. m height, 

 with a bawil breadth of 3 mm., tapering to 1-75 at the base of the 



tentacles. ^ e ^ ^ 



The tentacles are 2 mm. long and bear three rows of rounded 

 wart-like pinnules, leaving a triangular bare streak on both 

 surfaces There are about a dozen pinnules ni each longituclnial 

 row The pinnules appear very closely packed in slopnig trans- 

 verse rows of three. The whole surface of polyps and tentacles 

 is thickly covered by minute rod-like spicules (006 X 0-08), which 

 produce a somewhat glistening frosted appearance. Besides 

 these there are numerous zoochlorellse. 



This form resembles .Y. plicata Schenk in having rounded 

 wart-like pinnules in three rows, but difters in the shape of the 

 tentacles, the number of the pinnules, and the nature ot the 

 spicules (round or oval discs in X 'plicata). 

 Locality. Wasin Channel, 10 fms. 



Heteroxenia ELISABETHS Kolliker. 



A dense cluster of dimorphic polyps borne on a thick stelk 

 about 2-5 centims. in height, and 1 centim. in breadth. ihe 

 cluster itself has a diameter of 3-5 centims. The living forms 

 were white and grey in colour, and kept the tentacles continually 

 and rapidly opening and closing. 



The large polyps are numerous and marked by annulations 

 which are probably due to contraction. They vary from lo- 

 22 mm. in length, and from 2-2-5 mm. in breadth. The ten- 

 tacles in the fully matured polyps are from 5-5-6-5 mm. in length, 

 and 0-5 mm. in width. 



The pinnules are arranged in four rows on each side ot tlie 

 middle line, leaving both on the oral and on the aboral surface a 

 bare strip which stretches the whole length of the tentacle ihe 

 pinnules are 0-6-0-9 mm. in length, and from 0-05-0;2 mm. 

 in width. They are all long and slender, with the exception ot a 

 few wart-like pinnules at the proximal end. 



Besides the relatively distant large polyps, the crown bears 

 numerous small individuals which fill up all the gaps. Those on 

 the margin show tentacles with small wart -like pinnules arranged 

 in two rows. In a polyp 2 mm. long the tentacles are 0-8 mm. 

 in length, and show two rows of pinnules on each side with seven 

 pinnules in each row, leaving a narrow bare space on the oral 

 and a broad bare space on the aboral surface. iowarcls tiie 

 centre of the crown the majority of the small polyps show no 

 trace of tentacles or pinnules, but exhibit only a slight tendency 

 to be lobed at the margin. These are usually 4-5 mm. m length 

 and have semitransparent walls. _ 



Locality. Towards Kiungani, just below low tide 111 a fathom or 

 so of water. Previously recorded from Zanzibar and Port Denison. 



