212 



broad and somewhat broader upwards. Seen from above the 

 antheridia are more or less quadratic by mutual pressure. 



This species is found in much exposed localities and also in 

 quite sheltered. It occurs in shallow water and in deeper, down 

 to a depth of about 10 meters. 



It has been collected round St. Croix, at Xorthside, Longford, 

 Buck Island and in the Lagoon of Christiansted. 



Geogr. Distrib. West Indies, Vera Cruz, Red Sea etc. 



7. Dictyota crenulata J. Ag. 



J. Agardh, Nya alger fran Mexico (Ofvers. k. Vetensk., Akad. For- 

 haniU., 1847, p. 7). J. Agardh, Species Alg., vol. I, p. 94. J. Agardh, Till 

 Algernes Systematik, V, p. 99. A. Vickers, Phycologia Barbad., pi. XVI. 



In ''Species Alga- 

 rum", 1. c, J. Agardh 

 describes Dictyota cre- 

 nulata as : "pulchra et 



distinctissima spe- 

 cies" and in this I 

 agree with him. The 



specimens found 

 agreed well with the 

 figure of M'^s Vickers 

 (1. c). The plant is 

 rather regularly di- 

 chotomously ramified 

 and further characte- 

 rized by the presence 

 of numerous teeth, 



shorter or longer, 

 along the margin of 

 the frond. Compared 

 with original specimens from St. Augustin (Mexico) collected by 

 LiEBMANN, the Mexican specimens seem to be even more irregu- 

 larly dentate. 



In transverse section (Fig. 162) the frond is seen to be com- 

 posed of a medium layer of large, nearly quadrate cells sorrounded 

 by a layer of small epidermic cells. 



Both oogonia- and antheridia-bearing plants were collected; 



each kind of reproductive-organs occurs upon separated individuals. 



The antheridia (Fig. 162 6, Fig. 163) form small oval groups 



Fig. 162. Dictyota crenulata J. Ag. 



a, transverse section the thallus with oogonia. 



b, transverse section of the thallus with antheridia. 



(About 90: 1). 



