REVISION OF FRESHWATER SPONGES OF SPONGILLIDAE 11 



Gemmules abundant in mature sponge, scattered throughout its 

 body, spherical and large; pneumatic layer either well developed, 

 ill defined, or altogether absent. Whenever this layer is present, 

 gemmoscleres embedded in an irregular manner; as a rule absent when 

 this laj^er is lacking; foramen usually simple, or bearing a shallow 

 peripheral collar; diameter of gemmules ranging 500-800 n. 



Distribution. — Owing to previous taxonomic confusion of this 

 species with others, now belonging to another genus, S. lacusiris has 

 originally been considered a cosmopolitan species ; however, the present 

 studies were able to establish beyond doubt that it is restricted to the 

 Northern Hemisphere, with its greatest expansion in cold-temperate 

 regions. 



Color in life. — Usually drab to bright green owing to the presence 

 of a varying number of zoochlorellae. 



Discussion. — This species has been adequately described in pre- 

 vious literature, and the present studies have not revealed any ad- 

 ditional criteria for discussion. However, it is possible that future 

 studies of the material amassed will indicate a speciation trend in 

 distant populations, and in particular a closer study appears desirable 

 of those specimens (or races) which display a uniform character of 

 their gemmular pneumatic layer. At present no attempt is made to 

 indicate or demonstrate a possible subspecific status for these ap- 

 parently constantly differing forms, since specimens were examined 

 in which all the three types of gemmules mentioned above were 

 found to be present. Nevertheless, it seems interesting that the 

 majority of cold-temperate and subarctic specimens examined possess 

 gemmules with a rather ill-defined or absent pneumatic layer, a 

 feature apparently shared with those of S. arctica Annandale; whereas 

 the gemmules of most central and southern European specimens 

 display gemmules with a rather thick pneumatic coat possessing 

 a great number of gemmoscleres. Shoidd a future revision of this 

 material clearly indicate such a speciation trend, some of the old 

 "varietal" names such as S. I. paupercula (Bowerbank) and perhaps 

 also S. I. jor(/ane7isis Vej do vsky should be revived. The same applies 

 to a number of other species, described as such in previous literature, 

 and in particular to the S. lacustroides Kozhoff group of Asian sponges 

 here listed as synonyms of S. lacustris pending further detailed work. 



Since a type specimen apparently has never been designated, and 

 most certainly does not exist today, a neotype of Spongia lacustris 

 Linnaeus therefore had to be selected. This specimen is in the col- 

 lection of the Kijksmuseum van Natuurlijke Historic, Leiden, Reg. 

 No. 1053, coll. D. V. d. Kuyl, Vlaardingschevaart, Holland, 17. ix. 

 1941. The mode of growth and spicular components of this neotype 



279-430—68 2 



