BIOLOGICAL SURVEY OF WOODS HOLE AND VICINITY. 



537 



Pyramid Rock 



Chart 267. — Distribution of algseon Spindle Rocks, March 17, 1905. 



All the rocks were perfectly bare above low-water mark (the dotted line), having been scraped 

 clean during the winter by floating ice. Algse were present below low water only in positions where 

 they were protected from contact with the ice. The number of species on the rocks was small in com- 

 parison with other seasons of the year, and limited to those that may grow at some depth. 



It is interesting to compare the rocks above low-water mark, now entirely bare, with the conditions 

 on December 30, two and one-half months previous (chart 274), for at that date the rocks were covered 

 by growths of Cladophora lanosa var. uncialis (11), Phyllitis fascia (24), and Scytosiphon lomentarius (26). 

 The first zone of algae was well below low water and was composed of Ceramium rubrum (43), and Chon- 

 drus crispus (49), the last extending into deeper water. Somewhat away from the rocks or between 

 them were groups of Laminaria Agardhii (33), and occasional growths of Phyllitis fascia (24) and Scyto- 

 siphon lomentarius (26) were present. 



List of species: Ulva Lactuca, 4, few on Chondrus; Cladophora lanosa, 10; Ectocarpus siliculosus, 19, 

 on Scytosipkon; Phyllitis fascia, 24, few; Scytosiphon lomentarius, 26, few; Laminaria Agardhii, 33, groups 

 in deep water; Porphyra laciniata, 37, occasional; Callithamnion Baileyi, 41, on Ceramium; Ceramium. 

 rubrum, 43, abundant; Chondrus crispus, 49, abundant. 



