DIATOMACEiE FROM HERTFORD. 
199 
material subsequently collected, in the following June, in the same 
locality, which, in addition thereto, contained a number of large 
cysts of Synedra Ulna. In the same collection I also found examples 
of the sporangial development of several other species, amongst 
which were Gomphonema constrictum and Pinnularia viridula , and 
also some singular specimens of Odontidium mutabile , the constituent 
frustules of the filaments of which were of very unequal size. 
This condition is a most unusual one, as the filaments are generally 
of uniform width throughout, even if of considerable length. I 
can only account for it on the supposition that they were the 
result of sporangial development. 
With reference to the uses of the Diatomacese, and the place 
which they occupy in the economy of Nature, we appear to have 
but little knowledge. We cannot doubt but that they accomplish 
some useful purpose. Aggregated in numbers that defy all efforts 
of numerical computation, it is possible that by the absorption of 
carbonic acid and the production of oxygen, they may do much to 
maintain the purity of the waters in which they are found. 
LIST OF HERTFORDSHIRE DIATOMACEiE. 
Epithemia turgida, TV. Sm. 
,, granulata, Kutz. 
,, alpestris, TV. Sm. 
„ Sorex, Kutz. 
,, Westermanii, Kutz. 
,, gibba, Kutz. 
,, ventricosa, Kutz. 
,, Zebra, Kutz. 
Eunotia Arcus, W. Sm. 
Cymbella Ehrenbergii, Kutz. 
,, cuspidata, Kutz. 
,, ventricosa, Kutz. 
Amphora ovalis, Kutz. 
,, minutissima, TV. Sm. 
Cocconeis Pediculus, Ehr. 
,, placentula, Ehr. 
Cyclotella Xutzingiana, Thw. 
,, operculata, Kutz. 
,, Rotula, Kutz. 
Campylodiscus costatus, TV. Sm. 
„ spiralis, TV. Sm. 
Surirella biseriata, Be Breb. 
,, linearis, TV. Sm. 
,, splendida, Kutz. 
,, nobilis, W. Sm. 
,, craticula, Ehr. 
,, ovalis, Be Breb. 
,, angusta, Kutz. 
,, minuta, Be Breb. 
,, Amphioxys, TV. Sm. 
,, crumena, De Breb. 
Tryblionella gracilis, TV. Sm. 
,, angustata, TV. Sm. 
Cymatopleura Solea, TV. Sm. 
,, apiculata, TV. Sm. 
,, parallela, TV. Sm. 
,, elliptica, TV. Sm. 
Nitzschia sigmoidea, TV. Sm. 
,, linearis, TV. Sm. 
,, tenuis, TV. Sm. 
,, Amphioxys, TV. Sm. 
,, vivax, TV. Sm. 
,, dubia, TV. Sm. 
,, acicularis, TV. Sm. 
,, plana, TV. Sm. 
,, palea, TV. Sm. 
Amphipleura pellucida, Kutz. 
Navicula crassinervia, Be Breb. 
,, serians, Kutz. 
,, cuspidata, Kutz. 
,, rhynchocephala, Kutz. 
,, firma, Kutz. 
,, ovalis, TV. Sm. 
,, minutula, TV. Sm. 
,, affinis, Ehr. 
,, inflata, Kutz. 
,, gibberula, Kutz. 
,, amphirhynchus, Ehr. 
,, producta, TV. Sm. 
,, ambigua, Ehr. 
,, amphisbsena, Bory. 
,, sphaerophora, Kutz. 
„ pusilla, W. Sm. 
,, tumida, TV. Sm. 
,, dicephala, Kutz. 
,, cryptocephala, Kutz. 
