424 PETRIFACTIONS AND THEIR TEACHINGS. CHAP. V. 



discoidal ones, which are highly ornamented with radiated 

 markings. 



Pterichthys. On the uppermost shelves of the compart- 

 ment [2], there are several species of this genus, which, as its 

 name implies, has two wing-like lateral appendages. These 

 processes, like the spines of the Bull-head, (Coitus Gobio,) are 

 weapons of defence ; in some examples they are extended from 

 the sides at right angles. The head and anterior part of the 

 body are protected by large tuberculated scutcheons, and the 

 back and abdomen by angular plates : the tail is long and 

 angular, and supposed to have been the only organ of locomo- 

 tion. There are two eyes in front of the lateral appendages. 

 These Ichthyolites are only from two to ten inches in length. 



Coccosteus (Berry-bone-fish). 1 Wall-case A. [1.] This is 

 another allied genus, characterised by the tuberculated scales, 

 and remarkable dental organs ; neither eyes, nor pectoral fins 

 or spines, have been discovered. There are some good speci- 

 mens of these Ichthyolites on the uppermost shelf; their rich 

 purple and reddish colour arises from an impregnation of 

 phosphate of iron. There are three or four species, varying 

 from a few inches to two feet in length. The remains of this 

 genus are the most abundant of the ichthyic fossils in the 

 Devonian deposits. 



Pamphractus. Wall-case B. [2.] This is another genus 

 of small fishes belonging to this singular family; it is distin- 

 guished by the distinct separation of the cephalic region from 

 the thorax ; it had a pair of long pointed pectoral fins. The 

 specimen is from Dura Den, in Fifeshire. 



LEPIDOIDS. This family of ganoid fishes is extinct, but 

 existed in great force during the secondary epochs. It com- 

 prises sixteen or eighteen genera, which are divided into two 

 tribes according to the structure of the caudal fin; of the 

 homocer'cals (see ante, p. 421), of which there are twelve 

 genera; the most striking specimens in the collection belong 

 to Semionotus, Tetragonolepis, Dapedius, and Lepidotus. 

 The heterocercals amount but to six or seven genera ; among 



1 Mr. Hugh Miller's works should be consulted for details of structure. 

 The cranial bucklers of these Devonian Ichthyolites are admirably eluci- 

 dated in the last work of this powerful writer and able observer. See 

 " Footsteps of the Creator," pp. 5178. 



