THE STRUCTURE OF X ENIA HICKSONI. 185 



middle portion of the tentacle are about - 5 mm. long and '15 mm. to 

 •2 mm. broad, but those nearer the base and tip are smaller. The 

 pinnules when fully expanded are about three times as long as they 

 are broad, and each tapers gradually from its base to its blunt, 

 rounded tip. When slightly contracted the pinnule is somewhat 

 swollen at its base, and if further contracted becomes more swollen 

 and globular at its base as its length decreases. Although the body 

 of the polyp is non-retractile, the tentacles are often found slightly 

 contracted, being in many cases curled inwards over the mouth. 

 Several examples of tentacles in this condition are shown in Fig. 1. 



Diagnosis op the Species Xenia Hicksoni. 



The species of Xenia are distinguished from each other by the 

 general form of the colony, the size of the polyps and tentacles, the 

 number of rows and shape of the pinnules, and the presence or 

 absence of an area free from pinnules, on the inner face of the tentacle. 



After careful comparison with the accounts of all the hitherto 

 described species, I am unable to refer this specimen to any of them, 

 and therefore I have established for it a new species with the name 

 Xenia Hicksoni. Its characters are as follow : 



The colony consists of several cylindrical, usually branched stems, 

 arising from a single thick stem or base. The stems range in length 

 from 10 mm. to 30 mm., and in breadth from 4 mm. to 10 mm. From 

 the arched or convex summit of each stem the free parts of the polyps 

 arise. These are smaller and moderately close together near the edge of 

 the summit, but larger and further apart in the middle of the arched 

 end. The polyps (including tentacles) measure 6 mm. to 12 mm. in 

 length, and 1 mm. to 1*2 mm. in breadth. The tentacles are moderately 

 slender and 2 mm. to 5*7 mm. long. Each tentacle bears on the 

 inner side two series of pinnules, each series consisting of three rows 

 of twelve to twenty pinnules in each row. There is usually a narrow 

 area free from pinnules extending along the middle line of the tentacle 

 to within about 1 mm. of the tip. The pinnules are conical elevations 

 with rounded ends. Those in the middle of the tentacle are about 5 

 mm. long, and are about three times as long as they are broad ; those 

 nearer the base and tip of the tentacle are somewhat shorter. The 

 body-wall of the polyps is moderately thick, and is sti*ong enough to 



