208 



This species has been found near Buch Island at St. Croix in a depth 

 of about 5 fathoms and in several places in the sound between St. Jan 

 and St. Thomas. 



Geogr. Distrib. : The Atlantic coast of North America. 



4. Griffithsia spec. 



A single specimen of a sterile plant, which I suppose to be 

 a Griffiihsia, has been dredged in the sound between St. Thomas 

 and St. Jan, off Cruz Bay. 



The thallus of this plant is repeatedly pseudodichotomously 

 ramified, and has in the basal part large, nearly cylindrical cells, 

 about 300 400 /j. thick and 7 8 times as long. Towards the 

 summit the filaments taper gradually, the cells at the same time 

 becoming shorter; the uppermost cells are only about 150 tj. thick, 

 the top cell, when more developed, about 100 u only. 



It was found in a depth of about 20 meters. 



Subfam. 3. Mesothamnieae. 

 Mesothamnion nov. gen. 



Habitus frondis omnino Callithamnio similis, tetrasporangiis 

 etiam eodem modo dispositis et divisis ; differt autem ab hoc 

 genere corpusculis antheridiorum subcylindricis pedicellatisque et 

 procarpiis terminalibus cellulis auxiliaribus singulis instructis. 



Cystocarpia ex corpusculis 5 6 subglobosis, carposporas con- 

 tinentibus, composita, ramulis pluribus plus minusve involucrata. 



Mesothamnion caribaeum nov. spec. 



Planta in parte basali rhizoideis numerosis ramosis affixa; 

 caule non corticate quoqueversum lateraliter ramoso, cellulis fere 

 cylindricis in media parte ca. 450^ longis, 230 u latis. Kami 

 eodem modo ramulos gerunt, ramulis pseudodichotomis ex cellulis 

 cylindricis in media parte ca. 80 p. longis, 25 ij. latis compositis. 

 Tetrasporangia sphaerica triangule divisa, 45 it lata. 



Corpuscula antheridiorum subcylindrica, pedicellata, ca. 75 IJL 

 longa, 40 // lata. Cystocarpia satis magna ex pluribus corpusculis 

 plus minusve sphsericis et magnitudine diversis composita sunt. 



The thallus grows like a small shrublike tuft about 2 cm. 

 high. It is fastened to the host plant by means of a very rami- 

 fied root-system (Fig. 194 d). This consists, not only of the basal 

 ramified end of the main filament, but also of several vigorous 



