524 



POLYCYSTINA : FOSSILIZED DEPOSITS. 



whilst Dr. Wallich has met with this type abundantly in the Indian 

 Ocean. It appears to have been yet more abundant, however, 

 during the later Geological periods ; for not only have certain 

 forms (among them Haliornma, Fig. 266) been detected by Prof. 



Fig. 266. 



Fig. 267 



Haliomma Humboldtii. 

 Fig. 268. 



Perichlamydium pratextum . 



Fig. 269. 





Fig. 268. Stylodyctya gracilis. 

 Fig. 269. Astromma Aristotelis. 



