236 DBscBiraiVE catalogue 



Fracjilaria striolata, from the White Clialk of Gravesend, 

 Gallionella aurichalcea, from the White Chalk of Kiigen, 

 GaUionella sulcata, from the Chalk Marl of Caltanisetta, 

 Navicula ventrkosa, from the Chalk Marl of Oran. 



Cayeux (1892, 1897) has recorded numerous diatoms from 

 the Upper Cretaceous zones of Ammonites mammillaris and 

 A. inflatus in the Paris basin. lu his specimens the silicified 

 tests are sometimes replaced by calcareous matter. Hitherto 

 there are no authentic records of diatoms earlier than the 

 Upper Cretaceous. 



Order S1PH0NEACE.E. 



[Living family.] 



Unicellular Algae of very various size and external form. 

 The thallus may. be much branched and is often of considerable 

 size, but it is not separated by cell-walls into distinct cells. 

 Many of the genera are encrusted with a calcareous coating, 

 and the majority of them are marine. 



The Siphoneaoese are the most important group of fossil Algae, 

 and a number of well preserved and microscopically studied 

 forms have been described by B-othpletz, Steinmann, and others 

 from the calcareous members of the order. The soft-celled, 

 microscopic forms belonging to this affinity have not been re- 

 corded among fossils. 



Suborder CODIACE^S. 



Genus BOUEINA, Toula. 



[Toula, Sitzb. k. Akad. Wiss. Wien, math.-naturwiss. CI. 1884, 

 vol. 88, p. 1319. For the recognition of its plant-nature 

 see Steinmann, Bericht. naturf. Ges. Freiburg, vol. 11, 

 pp. 1-6, text-figs. 1-7.] 



The genus is monotypic and cannot therefore be diagnosed 

 apart from the species. It was described by Giimbel, Zittel and 

 others as a sponge, and the reference of the fossil to the Alga3 is 

 due to Steinmann. 



