REVISION OF FRESHWATER SPONGES OF SPONGILLIDAE 39 



thick; consisting of rather small polygonal air spaces; genimoscleres 

 embedded in this layer strictly tangentially in peripheral region; 

 foramen tubular, porus tube moderately long, rarely projecting beyond 

 surface of pneumatic layer. 



Distribution. — Known onlj^ from the type locality, Lampam, 

 Thailand. 



Color in life. — Recorded as brownish or clay colored. 



Discussion. — Annandale (1918a) and Gee (1932g) drew attention 

 to the similarity in skeletal characteristics of this sponge to the genus 

 Potamolepis Marshall, from which it derives its specific name. Annan- 

 dale furthermore recorded the apparent futility of retaining Potamo- 

 lepis as a distinct genus, which at present merely represents a some- 

 what artificial grouping of extremely to moderately hard spongillids 

 with stout amphistrungylous megascleres, the gemmules of which 

 have not yet been recorded. 



In order not to obscure possible taxonomic evidence, E. potamolepis 

 is here retained as a distinct species until a comprehensive revision 

 of all spongillids without recorded gemmules will become possible. 

 Following such a future detailed study it appears very likely that 

 most, if not all, species of the presently recognized genera Potamolepis, 

 Niidosjjongilla, Cortispongilla, and Pachydictyum will eventually be 

 distributed among those genera dealt with in this paper. The absence 

 of gemmules in the collections of species of the above four genera does 

 not necessarily mean that these asexual reproductive bodies have 

 not been produced. As in many spongillid species, but particularly in 

 the genera Eunapius, Stratospongilla, and Corvospongilla, gemmules 

 are known to adhere to the substratum to such an extent that they 

 can easily be left behind after the sponge has been dislodged. Future 

 more careful collecting efforts might yet succeed in locating such 

 "evasive" gemmules and in revising some problematic genera. 



Eunapius potamolepis is most closely related to a number of its 

 congeners, in particular to E. nitens and E. crassissimus. From the 

 fu'st it differs chiefly in the morphology of its genimoscleres, from the 

 second in its much more compact skeletal structure. At present the 

 relationship of this "group" cannot be fully elucidated. The amphi- 

 strongylous shape of the megascleres is perhaps of only little signifi- 

 cance, since in E. potamolepis amphioxea are often also present in 

 peripheral parts of the sponge skeleton, and in E. crassissimus the 

 majority of megascleres are at the most abruptly pointed amphioxea. 

 It is possible that future detailed ecological and morphometric studies, 

 apart from revealing speciation trends in distant populations of 

 "similar" species, will establish a number of distinct "modes of 

 growth" within one species. Until such additional evidence and data 

 become available, all efforts to clarify interspecific relationships 



