10 Dr. G. J. Hiiicle on some 7iew 



whilst the classificatoiy value of the gemmule-spicules is 

 generally recognized, it is an undoubted disadvantage to 

 rely wholly upon this single feature for generic distinction, 

 and may lead to uniting sponges in the same genus which in 

 other important features than those of the gemmule-spicules 

 are markedly different from each other. 



This is well exemplified in the case of the present genus 

 Uruguaya and certain species of Meyenia in which, as men- 

 tioned above, the gemmule-spicules are strikingly similar, 

 even in minute structural details, to those of Uruguaya, whilst 

 the skeleton-spicules and the characters of the skeleton are so 

 extremely different that they would fully justify retaining these 

 sponges in distinct genera. In these forms the converse of 

 Mr. Carter's statement occurs, since the gemmule-spicule is 

 more or less alike in all, and the skeleton-spicule and the 

 skeleton have undergone modification. Taking into account, 

 therefore, the cylindrical form of the skeleton-spicules in Uru- 

 guaya^ their peculiar fascicular arrangement in the skeleton, 

 and its firm rigid structure, this genus possesses characters, 

 independent of the gemmules, sufficiently distinct to mark it 

 off from other * freshwater sponges, and may properly be re- 

 tained. 



There can hardly be a doubt that such large branching 

 sponges as U. corallioides and U. Macandrewi result from an 

 uninterrupted growth of several years' duration, and that con- 

 sequently they must have lived in positions where they were 

 not exposed to those influences of heat, drought, or cold which 

 limit the existence of most freshwater sponges to a single 

 season. Their conditions of existence must in fact have 

 approximated closely to those of marine forms, and it is pro- 

 bably owing to these favourable circumstances that in one of 

 these species no gemmules have as yet been found, whilst in 

 another they are very sparsely developed. A further feature 

 in connexion with the gemmules is that they only occur in 

 the basal layer of the sponge, no trace of them appearing in 

 the branches and palmate extensions which grow from the 

 base and constitute the larger part of the sponge. In most 

 freshwater sponges the gemmules likewise occur in the basal 

 layer; but where there is a series of layers marking the 

 growth of successive years there is frequently, if not always, 



* I include under Uruguaya the sponges from the Pdver Congo 

 described by Dr. VV. Marshall under the genus Potamolepis (Zeitschrift 

 fiir Naturwissenschafteu, N. F. Bd. ix. p. 553). The author acknow- 

 ledges the generic identity of the Congo forms with JJrmjuuya, Carter, 

 but declines to adopt the name on account of its distinctive geographical 

 orie-in. 



