ROOM V. AGASSIZ'S CLASSIFICATION OF FISHES. 419 



British species form a large proportion of the Ichthyolites 

 illustrated and described by M. Agassiz ; and fortunately, in 

 our eminent Ichthyologist, Sir Philip Grey Egerton, Bart. 

 we have an able and zealous cultivator of this branch of 

 Palaeontology. 1 



AGASSIZ'S CLASSIFICATION OF FISHES. The four orders into 

 which the class PISCES is divided by M. Agassiz, are founded 

 on the following characters : 



Order I. PLACOID (from 7rAa|, a broad plate). The skin covered irre- 

 gularly with enamelled plates, sometimes of a large size, but frequently 

 in small points, as the shagreen on the dermal integument of the Sharks, 

 and the tubercles of the Mays. Lign. 82, fig. 4, a dermal spine from the 

 skin of a Ray. 



Order II. GANOID (ydvos, splendour, from the brilliant surface of the 

 enamel). The scales are of an angular form, and composed of plates of 

 horn or bone, covered with a thick layer of enamel, a structure which is 

 identical with that of their teeth. The Sturgeon is a living example of 

 this order. Lign. 82, fig. 3, is a fossil 

 scale of a fish of this division, the 

 Lepidotus. 



Order I II. CTENOID (ICTUS, a comb). 

 The scales are formed of plates, 

 which are toothed or pectinated on 

 their posterior margin or edge, like a 

 comb. As the plates are superim- 

 posed on each other, so that the 

 lowermost always extend beyond the 

 uppermost, their numerous sharp 

 points or teeth render the scales very 

 harsh to the touch. The Perch be- 

 longs to this order. Lign. 82, fig. 1, 

 represents a fossil ctenoid scale. LIGN. 82. 



Order IV. CYCLOID (KVK\OS, ILLUSTRATION OF THE SCALES IN THE 

 circle). The scales are composed of FOUR ORDERS OF FISHES. 

 simple laminae, or plates of bone or i. CTENOID. 2. CYCLOID. 

 horn/without enamel, and have smooth 3. GANOID. 4. PLACOID SPINE. 

 borders ; but their external surface is 



often ornamented with markings. The scales of the lateral line consist 

 of funnels placed one within the other ; the contracted part of which, 



1 The splendid and most important work entitled " Hecherches sur 

 les Poissons Fossiles, par Louis AGASSIZ," stands pre-eminent in this 

 department of science. It consists of five volumes, 4to. of letter-press, 

 and five volnmes folio, of coloured plates. It is the classical work in 

 this branch of natural history, and must be consulted by every one in- 

 terested in the subject. 



I would refer the reader for a condensed view of Fossil Ichthyology 

 to my " Medals of Creation," vol. ii. chap. xv. 



