2 



Fossil Fishes. 



Table-case, 

 No. 25. 



probable — that the ancestors of some of these soft-bodied types had 

 calcified dermal structures which have become fossilized and now 

 perplex us because there is nothing similar to them in the present 

 world. 



The earliest known fossils of this character seem to be the little 

 tooth-like bodies, first discovered in the Cambro- Silurian and 

 Devonian formations of Russia and North America, and named by 

 Pander "Conodonts" (Fig. 4). In external form, they are very 

 suggestive of the denticles of the Lampreys and Hag-fishes (Figs. 2, 

 3), but instead of being chitinous or horny, they consist of phos- 

 phate of lime. Dr. G. J. Hinde has also shown that they are 

 associated with little ornamented plates of similar structure and 

 composition, which have no analogues in the living forms just 

 mentioned. 



Fig. 4.—" Conodonts " from the Cambrian (after Dr. G. J. Hinde). x 10 times. 



Wall-case, 

 No. 1. 



The earliest evidence of fish-like vertebrates, other than "Cono- 

 donts," consists in a single head-shield of Scaphaspis kidensis, from 

 the Lower Ludlow of Leintwardine, Shropshire, discovered by Mr. 

 J. E. Lee, F.G.S. The next is met with in the "Ludlow Bone- 

 bed " of the Upper Silurian Formation. This thin layer consists of 

 fragmentary fish, crustacean, and other remains, among which have 

 been detected small, compressed, slightly-curved, and ribbed fish- 

 spines, named Onchns, and some minute shagreen- granules, called 

 Tkelodus, and a jaw- like fossil, with pluricuspid teeth, named 

 Plectrodus ; likewise the head-shields of a species of Scaphaspis, 

 and other similar fragmentary remains. 



Passing over the lower types and the Cyclostomata (Lampreys and 

 Hags) as at present too imperfectly known for systematic treat- 

 ment, we arrive at the second great order — that of the Plagiostomi, 

 comprising the Sharks and Pays. Next follow the Chim^eroidei, 

 only represented at the present day by the two genera of Chimaeras, 

 though constituting an important feature in most marine faunas 

 of past geological ages. The Dipnoi, or " Mud-fishes," follow, 

 and are specially noteworthy from the modification of the air- 

 bladder to perform the function of a rudimentary lung. Then 

 there is the order of Ganoidei — remarkable for the frequent 

 possession of highly-enamelled scales and head-shields — repre- 

 sented by innumerable hosts of extinct forms, both marine and 

 freshwater, but almost exclusively confined to a few river and lake- 

 dwelling types at the present time. And lastly, follows the equally 

 extensive order of bony fishes, or Teleostei, which exhibits its 

 maximum development in the existing fauna, and represents the 



