294 



F. BORGESEN 



4 (3—7) ce ^ s anc * are about 12 — 13 (J. thick. The cells in the main axis are 

 c. 20 jx thick and have a length of c. 40 [x in the middle of the axis. 



The tetrasporangia (Fig. 34 c) are terminal on the pinnules. They measure 

 35 X 27 ul. Thus, the tetrasporic plant seems to agree well with the Mediter- 

 ranean species, but for an exact determination sexual plants are essential. 



While our plant seems to have occurred in a very similar locality as 

 Ptilothamnion lucifugum Cotton, the Irish plant differs from the present one by 

 its bifid branchlets, agreeing in this respect with the Canarian Ptilothamnion 

 micropterum (Mont.) Born. Also Ptilothamnion bipinnatum (Collins and Hervey) 

 Howe differs much from the present plant among others by the ramose pin- 

 nules. 



Area of distribution: Mediterranean and adjacent parts of the Atlantic; 

 Easter Island. 



Callithaimiion Lyngb. 



C. paschale nov. spec. — Fig. 35. 



C. caespitosum, ca. 4 mm altum. Rami erecti in parte basali nudi, deinde 

 subdistiche ramosi. Rami alterni in plantis J*- et © simplices, in § superne pinnati. 



Cellulae majores in parte basali ca. 90 [X latae, in parte superiore gradatim 

 tenuiores et 15 ;x latis, apice ramorum late rotundato. 



Tetrasporangia obovata, ca. 58 [x longa et 47 ;x lata, et antheridia utraque 

 in interiore latere pinnularum posita. 



Cystocarpia gemina rotundata in pinnis subterminalibus sita. 



The height of the few plants I have seen only reaches about 4 mm. The 

 basal part consists of irregularly ramified decumbent filaments originating from 

 the lowermost cells of the erect filaments. These filaments are fastened to 

 the substratum by means of vigorous rhizoids (Fig. 35 d). 



From this basal system the erect branches grow up forming small tufts. 

 They are bare in their lower half, ramose in the upper. The branching is very 

 regularly distichous with alternating branches growing out from the upper end 

 of each cell. In the male and tetrasporic plants all the branches are simple. 



In the more vigorous female plant (Fig. 35 a) the branches in the upper 

 part of the plant repeat the ramification of the main axis. These branch- 

 systems of second order turn their edges against the mother branch, the whole 

 system lying in the same plane. 



In the main filaments the lowermost cells measure c. 90 jx across gradually 

 decreasing upwards, so that the tip is rarely more than about 15 |x thick. 

 The cells are rather short, general!} 7 only 1 — 1 V2 times their length. The top 

 cells are obtuse. Hairs do not occur. The cell wall is thick, attaining c. 4 jx 

 in the larger cells of the main filaments. 



As is usually the case in Callithamnion the tetrasporangia (Fig. 35 c) 

 occur on the inner side of the pinnules; they are obovate, c. 58 X 47 (x. The 

 antheridial stands (Fig. 36 b) occupy corresponding places, gradually covering 

 almost the entire upper side of the pinnules. 



