128 BRITISH MARINE ALGZ. 
alata. In Fig. 117, a, is a magnified branch, showing the manner in 
which the tetraspores are arranged on each sideof the midrib, when they are 
produced in the branches of this species. The variety angustissima is 
Fig. 116. Delesseria alata. 
the narrowest in the frond of any form of this species with which I am 
acquainted ; and so far as my experience goes, it is peculiar to the northern 
Fie. 117. (a) Branchlet of Delesseria alata; (b) D. ruscifolia; (c) vertical 
cutting of tubercle of Nitophyllum Gmelini. 
coasts of England. During two seasons of seaweed gathering, on the shores 
north of the Tyne, I always met with this extremely narrow form, and , 
never with the broader varieties which are common on the southern shores. 
