208 



The oogonia (Fig. 159 b) occur in the area of the frond be- 

 tween the series of hairs thus corresponding with the distribu- 

 tion of the tetrasporangia. They are found either in series and 

 then sometimes in two parallel rows, or they are often scattered 

 into numerous small roundish groups. The single oogonium is 

 pear-shaped cylindric with broad base ; it is about 80 fji long and 

 45 tji broad. 



Of this species 1 have also collected antheridia-bearing plants. 

 These were rather small, about 2 cm high, and have the antheridia 

 arranged in rather broad series alternating regularly with the 

 rows of hairs (Fig. 158) just as is the case of the tetrasporangia. 



The antheridia (Fig. 161) are of nearly cubic form, ca. 30 // 

 broad and 75// high; they originate from a surface cell and, just 

 as is the case with the mother cell of the tetrasporangia, so here 

 a small cell is cut off at the base. Sometimes I have found 

 antheridia also upon the lower face of the frond and correspond- 

 ing with the series upon the surface. No trace of oogonia were 

 found in these plants. M"® Vickers gives a picture of the 

 antheridia of this species but without any description. Judging 

 from the description by Hauck (1. c.) concerning P. dubia the 

 distribution of the antheridia in this species seems to come very 

 near to that in the present plant. On the other hand the 

 distribution of the antheridia in Padina Pavonia differs much 

 from our plant. Here the antheridia occur together with the 

 oogonia in the same plant and the antheridia form radiating 

 series at right-angle to the concentric series of oogonia^). 



This species occurs in the littoral and upper sublittoral 

 region in sheltered or somewhat exposed places. It has been 

 found with tetrasporangia in Dec. — March and with antheridia 

 in December. 



It is most probably a common species. St. Croix: Christiansted, 

 Longford, Great Pond. St. Thomas: Store Nordside Bugt. St. Jan: 

 Cruz Bay. 



Geogr. Distrib. West Indies. 



Dictyota Lamx. 



With regard to the determination of the species of this 

 genus I may point out that the very good figures in M"« Vickers 



') Reinke, J., Entwicklungsgescliichtliche Untersuchungen Uber die 

 Dictyotaceen des Golfs von Neapel. (Nova Acta d. k. Leop.-Carol.- 

 Deutschen Academie, Bd. XL, 1878, p. 24). 



