CERAMIACE^E. 239 



other extraneous matter that their tetraspores are fre- 

 quently destroyed. It was discovered by the Rev. Hugh 

 Davies on the Welsh coast, and is pretty generally dis- 

 tributed, though, from its small size, seldom found except 

 by accident. It is annual, and in perfection in summer 

 and autumn. The axillary position of the branchlets 

 gives the typical form of this plant a very distinct ap- 

 pearance ; but there are intermediate states which are 

 not easy to determine. 



Callithamnion virgatulum. The little twig Calli- 

 thamnion. 



Fronds about a quarter of an inch high, erect, growing 

 continuously or in tiny tufts, much branched ; branches long 

 and straight, spreading, alternate or on one side only • 

 branchlets consisting of a single joint, blunt, springing from 

 every articulation of the primary and secondary branches, 

 most frequently secund. Tetraspores formed from the 

 branchlets, sessile or on short stalks. 



The figure of this plant in Dr. Harvey's f Phycologia 

 Britannica ' is sufficiently distinct from that of C. 

 Daviesii, but it must be borne in mind that these repre- 

 sent extreme states of the two plants, and that there 

 exists an almost complete series of intermediate forms. 

 Dr. Harvey, "yielding to pressure from without," has 

 reluctantly awarded specific rank to C. virgatulum, but 

 Professor Agardh speaks of it only as a variety of C. 

 Daviesii. 



Callithamnion sparsum. The scattered Calli- 

 thamnion. 



Eronds about a quarter of an inch high, growing in minute 



