CORALLINACEiE 151 



Corallines. By this process they grow as hard as 

 stone, and have for this very reason contributed 

 largely to the formation of the Earth's crust. They are 

 known from very early periods in the Earth' s history , 

 for Lithothamnium jurassicum is already reported from 

 Jurassic strata ; in Cretaceous deposits they appear 

 plentifully, and in Tertiary times they were so numerous 

 that entire mountains were built up by them. The 

 well-known Latomien, near Girgenti, in Sicily, are 

 quarries in rocks consisting of Lithothamnia. In our 

 present day they continue their work, and occur in 

 enormous quantities, forming banks from the Poles to 

 the tropics, where they contribute largely to the build- 

 ing up of coral reefs. The late Mr. Foslie, the well- 

 known authority on Lithothamnioneae, kindly told me, 

 in a letter which he allowed me to quote, that the 

 number of known species was 276. Of these, ap- 

 proximately 12 are strictly Arctic or sub-Arctic ; 

 82 are limited to the tropics ; and 182 occur in the 

 temperate zones. For the Lithothamnioneae the rule 

 holds good as for other algae, from warm to boreal 

 or Arctic seas the number of species decreases, but the 

 number of individuals increases. 



The Corallinaceae are divided in many genera ; best 

 known are the slender and bushlike Corallina, Am- 

 phiroa, and Arthrocardia, and the encrusting or free- 

 branching Melobesia, Lithophyllum (Fig. 76), and 

 Lithothamnium (Fig. 75). The encrusting forms often 

 act like mortar to cement loose material together ; 

 the free branching forms develop into nodules even 

 bigger than a man's fist, and, cemented together, they 

 can form masses of more than a metre in diameter. 

 All Corallinaceae are fond of strong currents ; Corallina 

 and allied genera love places exposed to the surf of the 

 sea ; Lithophyllum and Lithothamnium prefer the 



