BIOLOGICAL STUDY OF TAP WATER. 415 
time ; but the exact harvest 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. 
DIATOMACEAE. 
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 Niayarae, Fragillaria Crotonensis, Frag. Gregoryana 
(= Dimeregramma Grunow), Frag. Capucina, Synedra radians, 
Synedra longissima, Synedra ulna, Cocconema parvulum, Coc. eymbi- 
forme, Coc. gibbum, Cymbella dicephala, Navicula radiosu, Nav: 
carassius, Nav. Rheinhardtii, Nav. Sauyerti, Nav. eryptocephala, 
Nitzschia lineata, Surirella pinnata, Sur. lineata, Coccone’s Thwaitsti, 
Voc. placentula, Cymatopleura ( Sphinctocystis) solea, Pleurosigma 
Spencerii, Gomphonema teneilum, Gomph. acuminatum, Gomph. con- 
strictum, Gomph. sp. ? Amphiprora ornata, Odontidium mutabile, and 
Encyonema caespitosum. 
Tn addition to the above the following have also been noticed :— 
Tabellaria flocculosa, Asterionella formosa, Meridion constrictum, 
Actynocyclus Niagarae, Nitzschia sigmoidea, Try/lionella gracilis, 
Epithemia turgida, Cymatopleura (Sphinctocystis) elliptica, Eunotia 
didyma, Melosira varians, and Melosira dentata, n. sp., with charac- 
ters as follows :—Filaments, slender ; frustules, scarcely twice as 
