410 VROF. J. a. THOMSON AND Mil. W. D. UENDERSON ON [Apr. 10, 



Older II. ALCYONACEA, Venill {pro parte). 

 Family X e n ii D /E. 



Xeiiia tmihellata Savigny. 



,, quhiqueserta May. 



„ memhrauacea Sclienk. 



„ cterulea Ehi'enberg. 



,, iernataua iScheuk, var. eloiKjata, iiov. 



„ rigida, sp. ii. 

 Heteroxenia elisahethce Kolliker. 

 Cespitidaria coerulea May. 



Note on the Species o/'Xenia. 



In the genus XeHia, as in the genus Clavularia, the question of 

 species is a ditticult one. All the species are within a I'elatively 

 narrow range, and the difierentifiting characters are, when taken 

 separately, somewhat trivial. Even in the same colony there are 

 sometimes noteworthy differences in the adjacent polyps — differ- 

 ences which are sometimes as marked as any one of the separate 

 items which are used to distinguish species. It seems likely that 

 many of the differences are purely rnodificational, and I'eferable to 

 diffei-ences in nutrition and the like. 



The number of rows of pinnvdes is a character which has been 

 much relied upon, but it is apt to lead one astray unless the 

 tentacles observed ai-e equally extended. Moreovei', there may be 

 3 rows at the proximal end and 4 about halfway up, or 2 at the 

 proximal end and 3 about luilfway up the tentacle. There can be 

 no confusion between a species with one row of pinnules on each 

 side and a species with four rows on each side, but to distinguish 

 two species because one has three rows and the other four 

 appears to us quite misleading unless this detail is supplemented 

 by many otheis. In X. umhellata we found fi'om 2-4 rows, in 

 X. quinqueserta 3-5 rows. 



Some workers have attached importance to the presence of wart- 

 like pinnules along with othei's of the usual elongated type ; but 

 the presence of a few wart-like pinnules at the proximal end 

 appears to us to be very common, and may be natui'ally expected 

 when a polyp is not fully grown. At the same time, the minute 

 warts of, foi' instance, X. rigida ai'e diagnostic in contrast to the 

 long pinnules of X. tmihellata. 



Another diagnostic featuie is the presence or absence of a bare 

 strip on the surface or surfaces of the tentacle, but this is apt to 

 be obscured or exaggeiated by the degree of contiaction. The 

 bai-e streak may be present at the proximal end and absent higher 

 up, or quite distinct along the distal half and cjuite obscui'ed by 

 contraction lower down. 



Xenia umbellata Savigny. 



The length of the stalls is 24'5 mm., with a maximum basal 



