EVIDENCE OP THE SILURIAN MOLLUSCS. 179 



molluscs, — terebratula and crania, — have been found, ever 

 since deep-sea dredging became common, to be not very rare 

 shells ; and in the Mediterranean, where they are less rare 

 still, fleets of Argonauts, the representatives of a highly or- 

 ganized family of the Cephalopods, to which it is now believed 

 the bellerophon of the Palaeozoic rocks belonged, may be seen 

 skimming along the surface, with sail and oar, high over the 

 profound depths in which they lie. And, of course, when 

 death comes, that comes to high and low, the remains of both 

 Argonauts and Brachiopods must lie together at the bottom, 

 in beds almost totally devoid of the intermediate forms. 



Now, the author of the " Vestiges," in maintaining his 

 hypothesis, suspends it on the handle furnished him by the 

 immense abundance of the Silurian Brachiopods. The Silu- 

 rian period, he says, exhibits " a scanty and most defective 

 development of life ; so much so, that Mr Lyell calls it, 'par 

 excellence^ the age of Brachiopods, with reference to the by 

 no means exalted bivalve shell-fish which forms its predomi- 

 nant class. Such being the actual state of the case, I must 

 persist in describing even the fauna of this age, which we now 

 know was not the first, as, generally speaking, such a humble 

 exhibition of the animal kingdom as we might expect, upon 

 the development theory, to find at an early stage of the his- 

 tory of organization." The reader will at once discern the 

 fallacy here. The Silurian period was peculiarly an age of 

 Brachiopods, for in no other period were Brachiopods so nu- 

 merous, specifically or individually, or of such size or import- 

 ance ; whereas it was not so 'peculiarly an age of Cephalopods, 

 for these we find introduced in still greater numbers during 

 the Liasic and Oolitic periods. In 1848, when Professor 

 Edward Forbes edited the Palaiontological Map of Britain and 

 Ireland, which forms one of the very admirable series of 

 " Johnston's Physical Atlas," the Cephalopods of the Silu- 

 rian rocks of England and Wales were estimated at forty- 



