1895.] MICROSCOPICAL JOURNAL. 273 



and these pools are very often rich in tlie very large 

 Pleurosigma balticum, var. maxime. The pools further 

 ba-ck that are fed by springs and are nearly fresh, con- 

 tain brown mud, and in them may sometimes be found 

 Pleurosigma terryanum ; I has^e found five sach 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 seals 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 apj)reciated 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 



