BRITISH DESMIDIE^E. 155 



15. DOCIDIUM, ^re6. 



Frond simple, straight, much elongated, linear, constricted at the 

 middle and truncate at the ends ; segments usually inflated at the 

 base. 



Fronds simple, straight, much elongated, sometimes even twenty- 

 times longer than broad, constricted at the middle, where the suture 

 is generally very distinct in both living and empty fronds. In almost 

 every species the segments are inflated at their base ; the ends are 

 truncate. 



Professor Bailey has been very successful in adding new and cu- 

 rious species to this genus, some of them differing greatly from any 

 previously known. 



Docidium, like Closterium, has terminal globules containing moving 

 granules, and its vesicles are either scattered or arranged in a single 

 longitudinal row. 



It differs from Closterium in its straight fronds and constricted 

 middle ; and from Penium it may be known by having a distant con- 

 striction at the middle and more elongated fronds. 



1. D. nodidosum (Breb.) ; frond stout; segments four to six times 

 longer than broad, constricted at regular intervals so as to produce 

 undulated margins ; sutui'c projecting on each side. 



Closterium Trabecula, Bailey, Amer. Bacil. in Amer. Journ. of Science and 



Arts, V. 41, p. 302. t. 1. f. 32? (1841). 

 Docidium nodulosum, Brebisson, in lit. cu7n icone (1846). 



Dolgelley, /. R. Durdham Down near Bristol, Mr. Thwaites. Aberdeen- 

 shire, Dr. Dickie and Mr. P. Grant. Ambleside, Westmoreland, Mr. Side- 

 hotham. Henfield, Sussex, and near Southampton, Mr. Jenner. 



Falaise, Brebisson. Maine to Virginia, Bailey. 



Frond large, distinctly visible to the naked eye, beam-like, constricted at 

 the middle, where the thickened suture projects on each side like an apiculus. 

 Segm.ents about four times as long as broad, scarcely attenuated, regularly in- 

 flated at intervals, whence the margins appear undulated ; the basal inflation is 

 the most prominent, the others less so as they are situated nearer the end ; 

 often only two or three nearest the base are distinct, but occasionally as many 

 as eight undulations may be counted at the margin. 



Docidium nodulosum differs from D. constrictum, Bailey, and D. nodoswn, 

 Bailey, in its more numerous but slighter constrictions. In both these species 

 the inflations are always four, conspicuous, and more distant. In D. verru- 

 cosum, Bailey, the segments are longer in proportion to their breadth ; the un- 



