510 KEPORT OX THE XEXIIDAE COLLECTED BY DR "WILLEY. 



The specimens referred to the three species X. umbellata, X. crassa, and X. 

 membranacea differ in one or more characters from the specimens described as tj-pical 

 of those species, but the differences are certainly not of sufficient importance to 

 justif)' the formation of new species. For example, the differences between the 

 specimen which is referred to the species X. crassa and the type specimen described 

 by Schenk, may be accounted for by the fact that Dr Willey's specimen is a young 

 colony the polyps of which have not yet acquired their adult size and characters, 

 while Schenk's was probably a more mature colony. It is therefore important to examine 

 and record the condition of the genital products of a colony in order that it may be 

 ascertained whether the polyps are, or are not, adult. Some of the differences between 

 Klunzinger's specimen of X. umbellata and the colony of this species in Dr Willey's 

 collection may also be attributed to differences in age (see p. 515), while others, e.g., the 

 form of the colony, may be due to the influence of dissimilar habitat upon the mode of 

 growth. It seems reasonable to suppose that specimens obtained from the Red Sea (eis 

 was Klunzinger's X. umbellata) and from New Britain may be subjected to rather 

 different external conditions, which may have an influence upon the colony, producing 

 variation in its general form, the stoutness of its polyps, etc. The photographs 

 coutained in Professor Hickson's Report on the specimens of Millepora collected by 

 Dr Willev show how manv different forms or facies mav be assumed bv a sinsjle 

 species. Some attention has been devoted to the anatomy of each species, but as 

 they all agree in their main features with X. Hicksoni, the anatomy of which has 

 been described in detail (Ashworth, 1S99) only a few notes on their structure are 

 appended. Important confirmation has been obtained of all the chief features de- 

 scribed in X. Hicksoni, with the exception of the giant flagella, which do not appear 

 to be present in any of these species. The most important point confirmed is 

 certainly the absence of ventral and lateral mesenterial filaments in which the polyps 

 of Xenia and Heteroxenia differ from those (autozooids) of any other Alcyonarian 

 hitherto described. 



XENIA CRASSA. Schenk. 



This species is represented by a small and probably young colony, the single 

 unbranched stem of which is thick, soft and fleshy and somewhat knob-shaped, its 

 polyp-bearing summit being convex. The height of the stem is 10 mm. — 11 mm. ; 

 its diameter at the base is 10 mm. and at the summit 15 mm. 



The polyps' are short and, stout and stand close together, especially round the 

 edge of the summit of the stem. The measurements of the larger polyps are — ■ 

 body of the polyp 3 mm. long and 1-5 mm. — 2 mm. broad (a very few polyps are 

 2-5 mm. in breadth), tentacles 2-5 mm. — 3-2 mm. long and 7 mm. — 12 mm. wide. Each 



' In order that the measurements and characters given below, may be compared with those given by 

 previous authors, the word polyp is used, in this and in similar connections in this paper, in the same sense 

 as these authors have used it, viz., to indicate the free or exsert portion of the polyp. It should be remembered 

 however that this is not the whole of the polyp, a considerable portion of it is enclosed in the stem from 

 the summit of which the free portion of the polyp projects, indeed a primary polyp (i.e. one of the first 

 formed polyps of the colony) extends down to the base of the colony. (See Plate LII. Fig. 7.) 



