IX GEOLOGICAL CONTEMPORANEITY 297 



specialised, or less embryonic, than Belemnites; 

 or the modern species of Lamellibranch and 

 Gasteropod genera, than the Silurian species of 

 the same genera ? 



The ANNULOSA. The Carboniferous Insecta 

 and Arachnida are neither less specialised, nor 

 more embryonic, than these that now live, nor are 

 the Liassic Cirripedia and Macrura ; while several 

 of the Brachyura, which appear in the Chalk, 

 belong to existing genera; and none exhibit 

 either an intermediate, or an embryonic, 

 character. 



The VERTEBRATA. Among fishes I have 

 referred to the Coelacanthini (comprising the 

 genera Ccelacanthus, Holophagus, Undina, and 

 Macropoma) as affording an example of a persistent 

 type ; and it is most remarkable to note the 

 smallness of the differences between any of these 

 fishes (affecting at most the proportions of the 

 body and fins, and the character and sculpture 

 of the scales), notwithstanding their enormous 

 range in time. In all the essentials of its 

 very peculiar structure, the Macropoma of the 

 Chalk is identical with the Ccelacanthus of the 

 Coal. Look at the genus Lepidotus, again, per- 

 sisting without a modification of importance 

 from the Liassic to the Eocene formations in- 

 clusivly. 



Or among the Teleostei in what respect is 

 the Beryx of the Chalk more embryonic, or 



