466 



DISTRIBUTION IN SPACE AND TIME 



unrolled species (fig. 1322), some even that were perfectly straight. 

 Such types may perhaps be regarded as unsuccessful attempts 

 at adaptation to changing surroundings. The Belemnites (fig. 

 1323) possessed internal shells, and in this and some other 

 respects, e.^. the possession of an ink-bag, resembled recent 

 Cuttle- f^ishes, though they belonged to a distinct group. Cuttle- 

 Fishes and Squids, which are now dominant members of their 

 class, were feebly represented in Mesozoic times, but as they 

 alone proved able, mainly by acquiring a rapid mode of swim- 

 ming, to fully adapt themselves to their environment, they finally 

 succeeded in almost entirely sup- 

 planting the more ancient types ^^^^}''i\*''^^s 



related to them. V^'iFi^ 



Fig- 132:;. — Uiiri.illed Cephalopods related tn Ammonites 

 [Haniiics left, Scapltites righLj, reduced 



Fig;. 1323.— Belemnites (reduced), i and 2, Res- 

 torations: ADC, internal shell; F, funnel; II, short 

 arms; K K, long arms; n, ink-bag; 3, shell. 



Although many of the primitive paLt-ozoic types of marine 

 Snails {Gastropoda) were able to maintain their foothold during 

 this epoch, the leading place was taken by specialized carnivorous 

 forms, which became more numerous and varied as time went on. 



Bivalves {Laine/Iibrauc/iia) played a much more important 

 part than in the preceding epoch, many new and more advanced 

 types coming into existence. The families now represented by 

 Oysters, Cockles, Mussels, and Razor-Shells, among many others, 

 first made their appearance. 



Mesozoic Fishes (Pisces). — The last marine representatives 

 of existing Limg-Fishcs {Dipnoi) existed in the earlier part of 

 the epoch, and some of the fossil teeth are so like those of the 

 Queensland Lung- Fish {Ccratodns) as to suggest a close relation- 

 ship with that form. There were many mesozoic Sharks, &c. 

 {Elasmobranchii), and we can trace the gradual specialization of 



