30 



III. — -A New Species of Gongrosira. 

 By G.^S. West, M.A. D.Sc. F.L.S. 



{Read December 19, 1917.) 

 One Plate. 



In September, 1916, Mr. D. J. ScourField forwarded me a lime- 

 incrusted alga for examination and possible identification. This 

 alga has proved of very great interest, and a detailed investigation 

 of its characters sliows that it belongs to the genus Gongrosira, but 

 that it does not agree with any of the described species. It was 

 found by Mr. D. J. Scourfield and Mr. G-. T. Harris on wood in a 

 stream at Weston Mouth, near Sidmouth, Devonshire, growinof 

 in such a position that it received the full force of the stream, 

 the water falling about two feet on to the incrusted alga. The 

 incrustation was from 4-9 mm. in thickness, somewhat nodular on 

 its upper surface, and of a vivid green colour. Mr. Scourfield kindly 

 provided me with a fine dried specimen of the calcified alga, one 

 fixed in formalin, and a living example in good condition. 



The genus Gongrosira was established by Kiitzing in 1843,* and 

 belongs to the sub-family Microthamniere of the Cha3tophorace?e, 

 the most important family of branched algse in the Ulotrichales. 

 Fully half the known species of Gongrosira are incrusted with lime, 

 but the alga collected by Mr. Scourfield and Mr. Harris differs in 

 many particulars from those previously described. 



The following is a diagnosis of the new alga : — 



Gongrosira scourfieldii sp. n. 



G. aquatica, in rivulis rapidissimis vigens, stratum efformans 

 vivide viridissimum circa 4-9 mm. crassum, calce valde incrus- 

 tatum; thalli pars inferior e filamentis densis anastomosantibus 

 constans, cellulis tumidulis irregularibusque, pars superior e fila- 

 mentis plus minusve erectis ramulosis, cellulis apicalibus obtusis 



* Kiitzing, Phycologia generalis,^1843, p. 281. 



EXPLANATION OF PLATE. 



Figs. 1-3. — Gongrosira scotirfieldii sp. n, x 500. 



1. Part of thallus, showing the nature of the branching. 2 and 3. Parts of 



'^the erect filaments, showing the intercalary zoogonidangia. 



a. Cell in which there is no pyrenoid in the chloroplast. b. Cell with two 



pyrenoids in the chloroplast. zg. Empty zoogonidangia. 



