McMURRICH. [VOL. II. 



and would probably be entirely out of harmony with the phylo- 

 genetic relationships of the genus. We have learned within 

 recent years how extensively nearly allied forms may differ, 

 and how great are the modifications which the hexactinian 

 type may undergo. The entire facies of Halcurias is that of 

 an hexactinian, and it may furthermore be pointed out that 

 instances of the occasional endocoelous development of mesen- 

 teries have been already recorded by G. Y. and A. F. Dixon 

 ('89) in Bunodcs thai Ha and by H addon ('98) in Actinioides 

 dixoniana and A. papuensis. 



If, then, the third possibility be excluded, Halcurias must 

 either be assigned to an existent family, the endocoelous 

 development of mesenteries being regarded as of minor im- 

 portance, or this feature may be considered of sufficient 

 importance to warrant the establishment of a separate family. 

 I have already indicated my belief that the peculiar mode of 

 development of the secondary and tertiary mesenteries is of 

 minor importance and see no more reason for separating Hal- 

 curias as the type of a new family than I do for separating an 

 octamerous sagartian, or one with a multiplicity of mouths and 

 many siphonoglyphs, from the rest of the members of that 

 family. 



It remains then to consider what the forms may be with 

 which Halcurias may be associated. As Carlgren has remarked, 

 and as I have indicated by the position to which I have referred 

 it in previous papers, Halcurias occupies a position near the 

 base of the hexactinian stem. The small number of perfect 

 mesenteries, the occurrence of reproductive organs on all of 

 them, the absence of a distinct sphincter muscle, the simplicity 

 of the margin, are features which, when combined in one indi- 

 vidual, indicate for it a somewhat low position. Are there 

 other forms which present a similar combination of peculiari- 

 ties associated with the development of an adherent base? 



Two forms suggest themselves in this connection, namely, 

 Go nactinia prolifera and ProtantJica simplex ; but both of these 

 present peculiarities which render their association with Hal- 

 curias inadvisable. They both have but eight perfect mesen- 

 teries, the remaining ones, eight in Gonactinia and about 



