POLYZOA OF WATERWORKS. 441 



It is a curious coincidence that, at the same Meeting of the 

 British Association at which Professor Hickson's address was 

 delivered, the Presidential Address of IMr. Charles Hawksley to 

 Section G (Engineering) dealt specially with water-supply and 

 the construction of waterworks. In this address it is stated 

 (Report, p. 767) that " mosfc waters obtained from gathering 

 grounds are much improved by filtration " ; and the mode of 

 construction of sand-filters is indicated. But there is no i-efer- 

 ence to the importance of the filter as a means of depriving the 

 water of the microscopic organisms which would otherwise supply 

 nourishment to Polyzoa and other " microphagous " animals 

 capable of flourishing in the pipes if they are supplied with 

 appropriate food in sufficient quantity. 



I am indebted to Mr. S. C. Chapman for having put at my 

 disposal the result of an extensive enquiry which he has made as 

 to the occurrence of Polyzoa and other animals in the waterworks 

 of this country. As he proposes to publish the result of his 

 enquiries I will not attempt to anticipate him; but he returns 

 show that organisms of the kind indicated occur more fi-equently 

 than has generally been supposed, and that the occurrence of 

 trouble due to their presence can usually be ti-aced to the want 

 of an efficient system of filtration. 



III. Species of Polyzoa found in British Waterworks. 



The species of Polyzoa which I have had the opportunity of 

 examining may be referred to the following four species : — 



(1) Paludicella articidata ^hrh. 



(2) Fredericella sultana Blumenbach. 



(8) Plumatella. fangosa Pall., var. coralloides Allman. 



(4) Plumatella einarginata Allman, var. viuseosa, Kraepelin. 



I subjoin a few notes on the synonymy of the species and on 

 the specimens which form the subject of this paper. 



(]) Paludicella articulata Ehrb. (PI. LXII. figs. 1-10.) 



Alcyonella articulata Ehrenberg, " Symbolas Physicae," "' Ani- 

 malia Evertebrata," Dec. 1, " Phytozoa Polj^pi," 1831, fol. a. 



Paludicella Ehrenbergii Dumortier & Van Beneden, " Hist. 

 Nat. des Pol. Comp. d'eau douce," ii. Partie, Nouv. Mem. Acad. 

 Bruxelles, xvi. 1843, p. 38. 



Although Allman, in his classical monograph (56) on the 

 Freshwater Polyzoa, accepted the specific name ehrenbergi — and 

 has been followed in this respect by many other writers — the 

 reasons given by Dumortier and Yan Beneden for rejecting 

 Ehrenberg's name are not in accordance with modern principles 

 of zoological nomenclature. They state as their motive for intro- 

 ducing a new name that " articulata " refers to a generic character, 

 and tiiei'efore cannot be used as a specific name. The invalidity 



