540 CORALLINACEAE. 



on the fronds of Zonaria sonalis along the South Shore (Phyc. Bor.-Am. 1950). 

 Its filaments are only 2 or 3 times dichotomous and 5-7 segments long. Its 

 segments are 3-4 times as long as broad and have about the same diameter as 

 those of C ruhens. The abundant conceptacles vary in form from turbinate 

 and flattened urn-shaped to fusiform-clavate and are Tu-f of a line long. The 

 type of the species grew on Turbinaria in the Eed Sea. 



Sub-class BACILLARIEAE (DIATOMEAE). 



This sharply defined group of minute organisms is of uncer- 

 tain affinities. By some writers it is included under the class 

 Algae ; by others, it is excluded. If included, it is here treated 

 in a rather unnatural sequence. However, a few words in regard 

 to the group may be here appended. 



The Diatoms are microscopic one-celled organisms that con- 

 tain in addition to chlorophyl a brown pigment related to that 

 found in the Phaeophyceae, though not identical with it. The 

 enclosing wall consists of two separable nearly equal parts, the 

 valves, one of which fits closely inside the other. The wall is 

 permeated with silica, which renders the valves almost imperish- 

 able, so that the Diatoms are abundantly preserved as fossils. 

 In most Diatoms the wall is regularly and beautifully marked 

 with pits, meshes, ridges, and furrows of various degrees of 

 delicacy. The Diatoms are very widely distributed, inhabiting 

 salt, fresh, and brackish water, and moist spots on the dry land. 

 They may float free at the surface, lie more or less free at the 

 bottom, or may be attached to the larger algae or other aquatic ob- 

 jects. Some species are solitary in habit of life ; others are associated 

 in colonies, which maj^ be ribbon-like, thread-like, or zigzag, or 

 may sometimes form branching gelatinous filaments imitating 

 an Ectocarpus or other filamentous brown algae. Many of the 

 free-living forms have the power of slow, irregular, spontaneous 

 locomotion when in contact with a solid substratum. 



The Diatoms are, as remarked, siliceous organisms and they 

 do not appear to be particularly abundant in calcareous seas like 

 that washing the shores of Bermuda. However, they seem to 

 have been little collected and studied in this region. So far as 

 known to the writer, only sixteen species of Diatoms have been 

 attributed to Bermuda. Most of these are listed in the papers 

 cited in the Bibliography under O'Meara and Castracane. The 

 type of Navicula Janischii Castr., now considered a form of 

 Dictyoneis marginata (Lewis) Cleve, was from Bermuda. 



