On the Phijlogenij of the Amijliidiscopliora. 47*J 



Hah. Oban, Eastern Southoni Nijicria. Alt. 000'. 



Type. Adult malo. ()rij::iiial n\iiiiljcr 7. Colle(;tc(l 13th 

 Au^Mist. 1900, by Mr. P. A. Talbot. 



TIk' brownish or ochrarcons belly of this form will readily 

 distiuijuish it from its ally the white-bellied F. leucostiyma, 

 as also will the diill-eoloiired median area of its tail. 



I have provisionally plaeed nl(/rens'ls as a subspecies of 

 mfni(//fi(/i), and talhoti of lencosti(jina, but it is (juite impossible 

 until immensely larj^er series arc? available to say how far 

 these allocations are likely to jjrove eorreet. It is a eora- 

 promisc between the old idea that all members of sueh a 

 j^roup as the present might be considered to be subspecies of 

 the parent form, and the practice of some of the American 

 zoologists, who app:'ar to restrict the use of trinomials to 

 such forms as no one but the author can distinguish, and he 

 only in certain lights. 



LVl. — On the Fhylogeny of the Amphidiscophora. 

 By R. KiRKPATRICK. 



(Published by permissiou of the Trustees of the British Museum.) 



The division by F. E. Schulze of the order Hexactinellida 

 into the two suborders Amphidiscophora and Ilexasterophora 

 was a great step in ailvance of previous classifications. 

 There are no known tran.sitions between the two great groups. 

 In several respects the Amphidiscophora have remained in 

 a more primitive condition. There is no evidence to show, 

 however, that one group ha^ arisen from the other, and conse- 

 quently a biturcation of the main stem is assumed. The 

 primary and essential character of the Amphidiscophora is 

 the presence of amphidisks ; what appears to be a second 

 character is the existence of genuine microhexactins (figs. 4, 5) , 

 which do not exist, so far as I have observed, in the Hexastero- 

 phora. (The small hexactins forming part of the framework 

 in Diclyonine s|jonges are not here regarded as micrc- 

 liexactins.) All so-culled " derived hexactins " in Hexasterc- 

 phora are hexasters with a single end ray to each main ray, 

 and have the axial canals terminating abruptly not far from 

 the centre of the spicule (fig. 3) *. 



* This is one reason aiuoiijr otliers for avoidiiifi tlio u.se of the "actin'' 

 ternaiiiulojry in de.-^cribintr tliese spicules, aud for usiiii,' the "a?ter" suHix. 

 In the Report on the ' Discuvt'ry ' Hexactinellida I have proposed the 

 term moi.ohe-xaster (/. e. niono.xyhexaster, monodi-jcuhexaster). 



