206 
DIATOMS : THEIR NATURE AND HABITS. 
the sewage-matter discharged into the river lower down. "With 
a view of obtaining some reliable information on this point, the 
diatomaceous forms from a number of these deposits were examined, 
with the result of finding numerous specimens of marine species 
even so high up as at Richmond. This indicated the power that 
the tide possesses of conveying solid materials far up the river, and 
suggested the probability that sewage-matter may have some con¬ 
nection with the formation of these banks. 
From these facts we perceive that the uses to which diatoms are 
applicable are of value and variety, and that the study of their 
nature and habits deserves careful attention. To the fact that such 
investigation is amply repaid by the interest which it inspires, I 
can bear full testimony, and can confidently recommend the study 
to all whose tastes incline towards microscopical science. Amongst 
the various problems yet unsolved in connection with the life-history 
of these minute organisms, those relating to their movements and 
reproduction offer exceptional opportunities for further research. 
I append a list of species found in Hertfordshire in addition to those 
enumerated by Mr. Robinson in 1883. 
Cymbella Ehrenbergii. 
Amphora minutissima. 
Cyclotella operculata. 
Surirella splendida. 
,, ovalis. 
,, Craticula. 
,, Amphioxys. 
Cymatopleura parallela. 
Nitzschia plana. 
,, tenuis. 
,, palea. 
Navicula spheerophora. 
,, dicephala. 
,, • pusilla. 
,, rostellum. 
Navicula Gastrum.* 
Pinnularia tabellaria. 
,, borealis. 
Synedra minutissima. 
,, pulchella. 
Gompbonema dichotomum. 
,, Cygnns (Ebr.) 
Odontidium Harrisonii. 
Himantidinm gracile. 
,, Arcus. 
Fragillaria capucina. 
,, virescens. 
Acbnantbes ventricosa. 
Orthosira arenaria. 
Melosira varians. 
* In lieu of Stauroneis truncata as previously recorded. 
