HALICKEASIDAE. 13 



01 



Vanhoffen distinguished two genera, Halicreas Fewkes and Haliscera, 

 basing the separation on the number of tentacles, Halicreas having more 

 than fifteen, Haliscera twelve or less per octant ; but I agree with Maas 

 (:05, p. 56) that a much more important character than the number of 

 tentacles is the presence or absence of the remarkable exumbral papillae. 

 If we employ this criterion the members of the family fall into two groups : — 

 on one hand the stem genus Halicreas with papillae, and on the other all spe- 

 cies without these structures. Maas believes that two genera should be distin- 

 guished for the species H. plaiygonon Maas, H. rotundaium Vanhoflfen, H. alba 

 Vanhoffen, H. conica Vanhoffen, and JI. racovitsae Maas, according as their 

 gonads are proximal, or occupy the central one third of the radial canals ; 

 but the degree to which the positions of the gonads may change with age in 

 other families (Geryonidae, Petasidae) suggests, that this character is of no 

 more taxonomic value than the number of tentacles ; thus, all Halicreasidae 

 with eight canals, with the tentacles uniformly arranged, but without ex- 

 umbral papillae, may be included in a single genus. It seems to me that 

 according to the ordinary rules of nomenclature the name Homoeonema of 

 Maas must be adopted for this genus rather than Haliscera of Vanhoffen, 

 inasmuch as Maas has demonstrated by a fresh examination of the type 

 specimens of Homoeonema plaiygonon, which he has designated as the type 

 species (: 06'', p. 3), is at least congeneric with the Haliscera alba of Van- 

 hoffen. The position of the two species referred by Vanhoffen (:02'')to 

 Homoeonema has already been discussed. 



It is probable that the new genus Botrynema, recently described by 

 Browne (: 08) from the collection of the " Scotia," in which the tentacles 

 are in groups, likewise belongs to this family. 



All of these three genera of Halicreasidae have eight canals. There is, 

 however, one species in the present collection undoubtedly to be referred 

 to this family because of the structure of its tentacles and otocysts, but which 

 has twenty-eight canals ; for this I propose the new genus Halitrephes. 



