SPONGES COLLECTED IN SCOTLAND. 245 



skeleton is formed, can usually be felt i£ they are held between the finger and 

 thumb, and in most cases it is possible to distinguish the spicules with the 

 aid of a hand-lens. Freshwater sponges should either be preserved in very 

 strong spirit — absolute alcohol if possible — or dried. I shall be glad to 

 examine and report upon specimens sent to me at Calcutta. 



Spongilla lacustris auctorum. 



This species, which is probably distributed all over the world, is extremely 

 variable in almost every character ; it is also, perhaps consequently, able 

 to survive in many kinds of environment, being found in brackish and 

 even salt water, in rivers, canals, lakes and small ponds. I have recently 

 found small but typical specimens in a pond in the Bombay Presidency, 

 while in Bengal two forms occur that may be no more than local races, 

 namely S. proliferens and S. reticulata. Apart from these, the closely related 

 S. alba of Carter is a common Indian species and has recently been recorded 

 from Africa*. In Europe and North America xS. /ac?/5i;n5 appears to be 

 commoner than any other freshwater sponge ; in India it is much less 

 abundant than the very distinct species S. carteri ; it has not as yet been 

 recorded from Africa but is known from South America, while several 

 closely allied forms, which may not be specifically distinct, occur in 

 Australia : as a fossil it has considerable antiquity. From Great Britain 

 the following recent species have been recorded as well as S. lacustris : — 

 Ephydatia Jiuviatilis, E. millleri, and Sj)ongilla fragilis ; while Tubella pennsyl- 

 vanica, Heteromeyenia ryderi, and a form probably conspecific with the North 

 American E2:>hydatia crateriformis, have been found in Ireland. Trocliospongilla 

 Jiorrida or erinaceus is the only other species known from Western Europe, 

 but has not as yet been recorded from the British Isles. S. lacustris may 

 be distinguished from all other species, in my opinion, by the following 

 characters : — The sponge is soft and easily compressed, bright green when 

 growing exposed to light ; as a rule a basal portion can be distinguished, 

 bearing long cylindrical branches. The skeleton spicules are sharply pointed 

 and smooth ; they are arranged so as to form distinct radiating fibres, 

 which are joined together by less distinct transverse fibres or by single 

 spicules in a network ; neither kind of fibre is very coherent. Numerous 

 minute, pointed, cylindrical flesh-spicules, which are more or less uniformly 

 covered with little spines, are scattered about in the substance of the 

 sponge and in the external membrane. The gemmules, which generally 

 have a yellowish colour, are spherical and open by a single aperture (in 

 var. midtiforis by several apertures) which is usually surrounded by a 



* As S. cerehellata, Bowerbank ; see Kirkpatrick, Ann. & Mag. Nat. Hist. (ser. 7) xx. 

 1907, p. 624. Although S. cerehellata is certainly a form of 8. alba, Carter, I cannot 

 agree that the latter is not distinct from S. lacustris, close ally as it is of this species. 



