160 THALLOPHYTA. [CH. 



long club-shaped terminations, and an inner region consisting 

 of loosely interwoven filaments. 



Codium Bursa L. and C. tomentosum Huds. are two well-known 

 British species, the former presents the appearance of a spongy 

 ball of cells, and in the latter the thallus is divided up into 

 dichotomously forked branches^ In this genus the thallus 

 is not encrusted with carbonate of lime, at least in recent 

 species. 



Sphaerocodium. Fig. 37, D. 



Rothpletz^ instituted this genus for certain small spherical 

 or oval bodies varying from 1 mm. to 2 cm. in diameter, which 

 have been found on crinoid stems or shell fragments of Triassic 

 age. Each spherical body consists of dichotomously branched 

 single-celled filaments, between 50 and 100/^ in breadth, and 

 from 300 — 500/x in height. The tubular cavities occasionally 

 swell out into spherical spaces which are regarded by Rothpletz 

 as sporangia. 



There is not sufficient evidence that Sphaerocodium Bor- 

 nemanni Roth, has been correctly referred to the Codiaceae. 

 The sporangia-like swellings described by the author of the 

 species are not by any means conclusive as characters of 

 important taxonomic value. Figure 37, D, illustrates the 

 ofeneral structure of the fossil as seen in a transverse section 

 of one of the calcareous grains. 



Like Girvanella, which has been referred by some writers 

 to the Siphoneae, Sphaerocodium occurs in the form of oolitic 

 grains. In the Triassic Raibler and St Cassian beds of the 

 Tyrol, as well as in rocks of Rhaetic age in the Eastern Alps, it 

 makes up large masses of limestone. Rothpletz compares the 

 structure of this genus with that of the recent alga Codium 

 adhaerens Kg., but it is wiser to regard such tubular structures 

 as Girvanella, Siphonema^ and Sphaerocodium as closely allied 

 organisms, which are probably algae, but too imperfectly known 

 to be referred to any particular family. 



1 Murray G. (95) PI. iii. figs. 1 and 2. 



2 Eothpletz (90), and (91) Pis. xv. and xvi. 



3 Bornemann (87) p. 17, PL ii. pp. 1-4. 



