C. Brodi@ei cannot be confounded with any of the species found at the Danish 
shores. C. corymbosum is the only species bearing equally numerous hairs but these 
hairs are much longer than in €. Brodiei. 
Localities. Kn: Nordostrev by Hirsholm, 7—9 meters depth, on Furcellaria fastigiata, July 
1904; one specimen with cystocarps met with at the same place in August 1922 (C. A. Jorgensen). 
3. Callithamnion tetragonum (With.) Ag. 
C. A. Agardh, Spec. Alg. Vol. II sect. I 1828, p. 176; J. Agardh, 1851, p. 53; Harvey, Phye. Brit. pl. 136, 
1849; Kylin, 1907, p. 158. 
Conferva tetragona Withering, Arrang. Brit. PL, 3¢ edit. Vol. IV, 1796, p. 405. 
Dorythamnion tetragonum Nägeli, 1861 p. 344—345. 
Callithamnion brachiatum Bonnem., Harvey, Phye. Brit. p. 137, 1849. 
This species is here taken in a somewhat wider sense than generally accepted. 
The typical, first described C. tetragonum is characterized by its thick pinnulæ, having 
Fig. 229. Fig. 230. 
Callithamnion tetragonum Ag. From Devonshire, Callithamnion tetragonum (f. brachiata). From 
ex herb. J. G. AGARDH. 47:1. Cherbourg. 47:1. 
their greatest thickness above the base (80—140 w according to Hauck, 75—100 u 
after KyLiN), consisting of barrel-shaped cells and suddenly acuminate. In the 
very nearly related C. brachiatum the pinnule are thinner (40—80 x) and consist 
of cylindrical cells 2—3 times as long as broad. This form is, certainly rightly, regard- 
ed as a form of C. tetragonum by several authors (J. AGARDH, 1. c.; Hauck Meeres- 
alg., p. 83; Gran, Kristianiafjord, p. 26); it forms further a transition to C. fruticulosum 
Ag., as principally known from the Scandinavian coasts. J. AGARDH has already 
stated that the latter is related to C. tetragonum, and Gran (1. c.) declares that the 
Norwegian specimens determined by him as C. tetragonum 8, brachiatum, show much 
D. K, D. Vidensk. Selsk, Skr., 7. Række, naturvidensk, og mathem. Afd. VII. 3, 41 
