FOSSIL FISHES. 



Another group (the Cyclostomata), having also a notochordal, 

 cartilaginous skeleton, may perhaps, like the " Lancelet," have 

 been present amongst the earliest living forms. The only hard 

 structure which they possessed consisted of minute horny denticles 

 with which the mouths of some of them were armed. Small 

 serrated bodies, having some resemblance to the horny dental plates 

 of the "Hag-fish, " Myxine (Fig. 2), have been met with in the 

 Cambro-Silurian and Devonian formations of .Russia, England, and 

 North America (Table-case No. 25) ; they are called " Conodonts " 

 (Fig. 4), and may perhaps attest the occurrence of these simple 



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



Cyclostomatous fishes in the lower Palaeozoic rocks.* The earliest 

 evidence of fossil fish-remains, other than " Conodonts," is that of 

 a single head-shield of Scaphaspis ludensis, from the Lower-Ludlow 

 Rock, of Leintwardine, Shropshire ; discovered by Mr. J. E. Lee, 

 F.Gr.S. ; the next is met with in the Ludlow " Bone-bed " in the 

 Upper Silurian Formation (Table-case No. 25). This thin layer 

 consists of fragmentary fish, crustacean, and other remains amongst 

 which have been detected small, compressed, slightly curved, and 

 ribbed fish-spines, named Onchus, and some minute shagreen-scales, 

 called Thelodus, and part of a jaw-like organism, with pluricuspid 

 teeth, named Plectrodus, likewise the head-shields of a species of 

 Scaphaspis, and other similar fragmentary remains. 



The spines and scales may have belonged to one of the Plagio- 

 stomatous fishes, such as the Sharks or Rays. 



Passing over the first and second sub-classes (I. Leptocardii 

 and II. Cyclostomata — the latter of which is only doubtfully 

 represented by the above-mentioned bodies known as "Conodonts") 

 — we arrive at the third great sub-class, the Pal^ichthtes, embrac- 

 ing all the more ancient fossil fishes ; subdivided into the Chondro- 

 pterygii, comprising the Sharks, Rays, and Chimeras ; and the 

 Ganoidei, embracing the great majority of the fossil fishes whose 

 remains are met with in the Palaeozoic and Mesozoic formations. 



The latter are characterized by their highly enamelled scales or by 

 the head-shield and bony-plated cuirass with which some of them 

 are covered. 



The fourth great sub-class, named the Teleostei, includes all 

 those fishes with a true bony skeleton. It is in this division that 

 most of the Tertiary and existing species of fishes are placed. 



* See Dr. G. J. Hinde's paper in Quart. Jour a. Geol. Soc, 1879, Vol. XXXV., 

 pp. 351-369, Pis. xv. xvi. and xvii., on Cambro-Silurian and Devonian Conodonts. 



