BIOLOGICAL STUDY OF TAP WATER. 415 



time ; but the exact haiwest time of each particular form has not 

 been accurately determined, since the observations have not been 

 sufficiently close. For the same reason, although the comparative 

 frequency of most of the forms met with can be indicated gene- 

 rally, their relative abundance or scarcity at any particular time 

 cannot be stated with any degree of accuracy. 



To the foregoing general remarks is now added an enumeration of 

 the different organic species which from time to time I have found in 

 the tap water of the School of Practical Science, with brief notes on 

 some of the more interesting forms, and a more detailed account of 

 >one or two which I believe to be hitherto undescribed. 



DlATOMACEAE. 



The Diatoms are noticed first because by far the greatest part of 

 the sediment consists of them, and because in the number of species 

 they greatly exceed any other group. The diagnosis of species unless 

 one is a specialist in this department of microscopy, is not a very 

 easy matter, especially if the literature to which one has access is 

 not very extensive. Accordingly a slide was prepared and sent to 

 Prof. H. L. Smith, of Hobart < 'ollege, Geneva, N. Y., who kindly 

 named the following species : — 



Melosira Crotonensis, Tabellaria fenestrata, Cyclotella Kutzingiana, 

 Cyc. operculata, Cyc. astrea (a variety of Stephanodiscus Niagarae), 

 Stephanodiscus Niagarae, Fragillaria Crotonensis, Frag. Gregory ana 

 ( = Dimeregramma Grunow), Frag. C apucina, Synedra radians, 

 Synedra longissima, Synedra ulna, Cocconema parvulum, Cog. cymbi- 

 Jorme, Coc. gibbum, Cymbella dieephala, Naviada radios", Nav- 

 carassius, Nav. Rheinhardtii, Nav. Saugerii, Nav. cryptoa-phala, 

 Nitzschia lineata, Surirella pinnata, Sur. lineata, Cocconeis Thwaitsii, 

 Coc. placentula, Gymatoplenra ( Sphinctocystis ) solea, Pleurosigma 

 Speneerii, Gom)>honema tenellum, Gomph. acuminatum, Gomph. con- 

 strictum, Gomph. sp. ? Amphiprora ornata, Odontidium mutabile, and 

 Encyonema caespitosum. 



In addition to the above the following have also been noticed : — 

 Tabellaria floculosa, AsUrionella, formosa, Meridion constrictum, 

 Actynocyclus Niagarae, Nitzschia sigmoid ea, Tryblionella gracilis, 

 Epithemia turgid a,, Cymatopleura (Sphinctocystis) elliptica, Eunotia 

 didyma, Melosira varians, and Melosira dentat'i, n. sp., with charac- 

 ters as follows : — Filaments, slender ; frustules, scarcely twice as 



