GEOLOGICAL HISTORY 49 



including the freshwater Cyrenidae, made their 

 appearance ; while if Corburella be admitted as a 

 member of the Septibranchia, that order must be 

 added for the first time. The " pens " and ink-sacs 

 of earlier members of the Sepia tribe (Beloteuthis and 

 Geoteuthis) are first found in the Lias, with the 

 remarkable Belemnites whose " guards," often called 

 " thunder-bolts," are familiar fossils. 



In the succeeding Cretaceous period further de- 

 velopment took place. Among the Gastropods there 

 was a decided increase in the higher Pectinibranchs, 

 including representatives of most of the families of 

 Rhachiglossa. Amongst Bivalves two most remark- 

 able aberrant families (Radiolitidae and Hippuritidae) 

 were confined exclusively to this period. Externally 

 these look not unlike simple corals with a lid, while 

 internally they display highly peculiar modifications. 

 Numerous other Eulamellibranchs, including some 

 boring forms such as Petricolidse and Saxicavidse, 

 as well as the Razor-fish (Ensis), arose, with an 

 undoubted representative of the Septibranchs (Leio- 

 pistha). An Octopus (Palceoctopus Newboldi) standing 

 for the highest Cephalopods was revealed for the 

 first time in the Cretaceous of Mount Lebanon, but, 

 on the other hand, the Ammonites and Belemnites 

 died out. 



During the Tertiary epoch the Rhachiglossa and 

 Toxoglossa became the dominant Gastropods, while 

 the Bivalves showed an approximation to present 

 4 



