170 SEAWEEDS 



established on insufficient grounds. Urospora and 

 Gomontia have as yet been recorded only in Europe, 

 but the latter has probably a much wider area. All 

 the genera are represented in British seas. 



ULOTRICHACE.E. 



General Characters. The genera here brought 

 together are usually classified as follows : Ulothrix 

 under Ulotrichacece, and Checteffara, Bolbocoleon, 

 JEntoderma, Epidadia, Phceophila, Acrochcete, and 

 AcroUaste under Chcetophwacecc. The limits between 

 these two orders are, however, hard to define, and 

 they do not appear to rest on very weighty characters. 

 Both are much more largely represented in fresh- 

 waters with numerous generic types not occurring in 

 the sea, and a discussion of the propriety of treating 

 these orders as one or separately is out of place here. 

 There is certainly no strong reason for separating by 

 ordinal division the genera dealt with here. The 

 thallus is a simple branched or unbranched cell-row, 

 with one nucleus in each cell, and the reproduction 

 is by the conjugation of equal gametes with two 

 cilia, and non-sexually by zoospores with two or four 

 cilia. Vegetative forms of propagation are also 

 known. 



The Thallus. In Ulothrix the thallus consists 

 ordinarily of a single cell-row, attached at the base 

 by a holdfast. The cells are all equally capable of 

 division, except the basal one, which is generally 

 more elongate than the others. Chcetophora is very 



