1895.J MICROSCOPICAL JOURNAL. 273 



and these pools are very often rich in the very large 

 Pleurosigma balticum, var. maxime. The pools further 

 back that are fed by springs and are nearly fresh, con- 

 tain brown mud, and in them may sometimes be found 

 Pleurosigma terryanum ; I have found five such pools on 

 the Conn, shore many miles apart, in which this Pleuro- 

 sigma may be gathered nearly pure ; with this may often 

 be found Surirella striatula, Navieula maculata and N. 

 permagna with Nitzschia scalaris and many species of 

 Amaphora and Amphiphora and smaller species in abun- 

 dance. The second class of pond holes are sometimes 

 larger than the first, but are shallow and the bottom is 

 formed of peat; these show where the sea is recovering 

 possession of the marsh by the subsidens of the coast, 

 and are recent formations ; they seldom contain large 

 diatoms. 



In exploring the marshes for diatoms it is necessary 

 to go at low tide. While collecting I generally visit them 

 day after day for weeks, bringing in a mass of material 

 each day of from ten to twenty pounds in weight, and 

 in making soundings in the bays and coves a much 

 larger amount of material has to be examined. A pre- 

 liminary examination will frequently show the general 

 character of the gathering, but a thorough cleaning of 

 each sample is necessary to determine the species con- 

 tained in each. The amount of labor involved in this 

 work can only be aj^preciated by those who have had 

 practical experience in it. It is a simple matter to pick 

 up a tuft of sea- weed on the beach and from it to make 

 out a formidable list of species, while the whole amount 

 obtained may not be enough to make a half dozen slides. 

 It is a very different thing to clean and examine such a 

 mass of material collected systematically from every 

 part of the locality and from different depths of water. 

 Notwithstanding the care with which I have gone many 

 times over the ground I have no doubt but that it might 



