238 "ENDEAVOUR" SCIENTmC EESULTS. 



various. The megasclen's arc of two kinds o}tJy : in 

 addition to acantho styles there arc smooth or terminally 

 spined, typically slender, monactinal, or oxeote or tornotc 

 qnasi-diactinal, spicules zvhich occur inter stitially and 

 dermally and usually also within the fibres as coring 

 spicides. The microsclcres [if present) are isochelce and 

 {or) toxa or sigmata. 



I propose to revive the generic name Ullsonella, and to 

 include thereunder, provisionally, a somewhat heterogeneous 

 assemblage of species which hitherto have been wrongly as- 

 signed to Clathria. The single characteristic common to all 

 of these, which distinguishes them from species proper to the 

 latter genus, is a deficiency in spiculation due to the absence 

 of those megascleres apparently, which, in the case of normal 

 Myxillinze, are termed the principal. 



The proposal is the outcome of an attempt to secure the 

 remoxal from Clathria of certain species {e.g., Jlllsonclla 

 curvichela, sp. nov.) which are peculiar not only in the lack of 

 principal megascleres but also in the possession of arcuate 

 chelae. Palmate isochelae, varying but slightly in form, are 

 so characteristic of Clathria and related genera, that the oc- 

 currence in the species referred to, of strictly arcuate chelae, 

 is in itself satisfactory proof of their rather wide separation 

 phylogenetically from typical members of the genus. Of the 

 propriety of the removal of such species, therefore, there can 

 be no question ; but, unfortunately, owing to the existence ol 

 species devoid of microscleres and of species in which the 

 chelae are of apparently intermediate or ambiguous form, this 

 difference in the character of the chelae proves to be lacking 

 in practical value for the purpose of generic definition. Con- 

 sequently, so long as generic distinctions continue to be based 

 solely upon skeletal and spicular characters, the separation 

 from Clathria of W. curvichela and its allies can be effected 

 only by taking advantage of their peculiarity in the first- 

 mentioned respect — a peculiarity, however, which is also ex- 

 hibited by a number of unrelated species, including amongst 

 them several with palmate isochelse ; and the question thus 

 arises as to which alternative has most to recommend it, (i.) 

 the association together in a single genus apart from Clathria 

 of all the species distinguished by the absence of spicules 

 identifiable with principal megascleres, or (ii.) the continued 

 retention of all such species within the genus Clathria. So far 

 as I have been able to obtain information of species thus dis- 

 tinguished, it seems to me, inasmuch as each of them differs 

 also in other important respects from typical species of 

 Clathria, that the former course (until a more extended know- 

 ledge points the way to a better scheme for their disposal) is 

 to be preferred ; hence the proposal to unite them under 



