20 NATURAL SCIENCE. July. 1894. 



A. Coloured Plants — continned. 



2. Chlorophyceas (Green algae). 



i. Filaments segmented. 



a. Filaments monosiphonous, conferva-like. 



a. Joints often irregular; branches separated at the base by a wall. — 



Gomontia. 



b. Joints regular, cylindrical; branches without basal wall. — 



SipJionochidiis. 

 ^. Filaments anastomosing, producing parenchymatous expansions. — 



Zygomitiis. 

 a. Filaments unsegmented. — Ostreobium. 



3. Phycochromacese or Cyanophyceae (Blue-green algae). 



a. NostocacejE. 



/. Filaments very much branched, provided with hairs and lateral hetero- 



cysts. — Mastigocoleus. 

 ii. Filaments simple or little branched ; without heterocysts and hairs. 



a. Filaments very fine, 0-95 to 15 /j. thick, branched' — Plectonema. 



|3. Filaments simple, 4-6 ^t thick, a fresh-water plant. — Phormidiiim. 



b. Chamaesiphonaceae. 



Trichomes composed of distinct cells, contents of which finally divide 

 into secondary cells. Plant very refractive. — Hyella. 

 B. Plants Colourless, appearing to belong to the Fungi. 



1. Filaments very fine, straight, uniform, unsegmented. — Ostracoblabe. 



2. Filaments irregular, presenting globular swellings. — Lithopythiimi. 



Perforating Thallophytes (algse and fungi) have been found in 

 foraminifera, corals (recent and fossil), calcareous pebbles, fish-scales, 

 and molluscan shells (empty and living), and may yet be found in 

 calcareous rocks. They are to be found from the littoral zone to a 

 depth of 1,095 fathoms, from the Arctic regions to the Equator, and 

 14° S., and at Cape Horn. They occur in sea- and in fresh-water. 

 Some genera are extremely rare, having been seen on one occasion 

 only. Others are very common. Thus, on the northern shore of 

 DubHn Bay I should have no great difficulty in obtaining a thousand 

 specimens of the razor-shell and others attacked by Gomontia, and, in 

 all stages of disintegration, as a result of its boring activity. There 

 can be no doubt that there is every probability of large additions to 

 our knowledge of the group by painstaking inquiry, both in the com- 

 pletion of the life-histories of the forms already made known, and in 

 the discovery of new species. 



REFERENCES. 



1. Natural Science, " The Growth of a Madrepore Coral," Feb., 1894, p. 85. 



2. Bornet et Flahault. — " Sur quelques plants vivant dans le test calcaire des 



mollusques." Bull. Soc. Bot. France, t. 36, 1889, pp. 147-176, plates vi.-xii. 



3. Duncan, P.M. — "On some Thallophytes Parasitic within Recent Madreporaria." 



Proc. Roy. Soc, 1S76, no. 174. 



4. Lagerheim. — " Note sur le Mastigocoleus." Notarisia, 1886, i., p, 65, tab. i. 



5. Batters, E3. A. L. — Conchocelis rosea (a perforating red alga) . Phycological 



Memoirs, ii., 1S93. 



T. Johnson. 

 The Laboratory, Glasnevin, Co. Dublin. 



