THALLOPHYTA 



37 



3. Red algae. — The lime-secreting types of these algae are the 

 " nullipores " or " corallines." They include among others, — 



a. Corallina. This plant grows in delicate jointed filaments 

 which form little tufts on rocks and seaweeds in tide pools along 

 the northern Atlantic Coast. The white incrustation of its 

 fronds gives it a coral-like appearance. Primicorallina is a 

 distantly related form from the Ordovician (Fig. 8). 



b. Lithothamnion. This usually forms crusts on the surfaces 

 of shells, corals and rocks (Fig. 9, C). On the coast of Spitz- 

 bergen, for example, it covers the bottom in deep layers for many 



Fig. q. — Comparison of the ancient Cryptozoon with the modern alga, Lithotham- 

 nion. A, Cryptozoon bassleri Widsind ( X ^), from the Cambrian of Pennsyl- 

 vania. The vertical transverse section shows the successive laminae of growth. 

 B, Cryptozoon proliferum Hall, from the Beekmantown (Lower Ordovician) of 

 Pennsylvania. The transverse section ( X 6) shows what may be spore cases 

 {s.c). C, Lithothamnion living off the coast of Eastport, Maine. The vertical 

 transverse section ( X I2) shows the growth laminae and the spore cases. {A and 

 B after Wieland.) 



miles, the material for future strata of the earth's crust. Some 

 globular arctic species reach a diameter of six to eight inches. 



