CRETACEOUS PERIOD 107 



mistakably before the Jurassic. Once established they seem 

 to have advanced rapidly ; and they were present in Creta- 

 ceous seas with carapaces variously shaped. Some of the 

 creatures apparently were very similar to the modern sponge- 

 crabs ; and possessed special limbs for holding a sponge or 

 other marine organism on the back for self-concealment 

 (Dromiopsis). Other forms seem to have closely resembled 

 the shore-crabs, masked-crabs, and frog-crabs of our own 

 time (Necrocarcinus, Palceocorystes, Raniella). 



Some barnacles were now to be seen directly fixed to their 

 haunts by means of cement, the stalk apparently having 

 gone to waste (Verruca). This method of attachment no 

 doubt saved the animals some exertion ; and life in barnacle 

 circles became more inert than ever. 



Whilst crustaceans were thus advancing, hard times had AMMONITES 

 set in for most of the cephalopods. The ammonites, it will 

 be remembered, had a large measure of prosperity in the 

 Jurassic Period ; but clear signs were not then wanting of 

 impending trouble. Matters became far more serious in the 

 Cretaceous ; and the resources of these enterprising molluscs 

 were tried to the uttermost. Surely no creatures ever battled 

 more strenuously with adversity. Some appear to have 

 wooed Fortune with elaborate ornamentations of the shell 

 (Hoplites, Douvilleiceras]. Many ceased indeed to be ammon- 

 ites in the sense of creatures with shells suggestive of a ram's 

 horn. Some forms had their shells twisted into little towers 

 (Turrilites). Others were more or less uncoiling themselves 

 reversing engines, as it were, in view of dangers ahead 

 (Hamites, etc.). Some indeed had become completely uncoiled 

 (B acuities}. But whatever their adaptations, ammonites con- 

 tinued to decline ; and in the next Period this once great 

 Order was represented by a mere remnant of moribund 

 forms. 



The squid-like Belemnites well maintained their position BELEMNITES 

 for a time ; and many new forms made their appearance. 

 Curiously enough when their arch-enemies, the Ichthyosaurs, 

 were in extremis, they themselves commenced to decline. 

 Gradually dwindling down to a few genera, they became at 

 the close of the Period wellnigh extinct. 



