ORDERS OF FISHES. 149 



Old Eed Sandstone ; but the genus appears to have entirely 

 disappeared before the close of the Devonian period. 



In the genus CoccosUus (fig. 514) the head was protected 

 by a great shield, the plates of which are covered with small 

 hemispherical tubercles. There is also a ventral or " sternal " 

 sliield, which, according to Huxley, seems to have had no 

 direct connection with the cephalic buckler. The mouth was 

 furnished with a distinct lower jaw or " mandible," composed 

 of two rami, carrying small teeth. The notochord was per- 

 sistent, but the neural and haemal spines of the vertebra?, and 

 the rays of the dorsal and anal fins, are well ossified. A 

 heterocercal tail-fin was doubtless present as well. The genus 

 Coccosteus is essentially Devonian ; but a species has been 

 discovered by M. Barrande in the Upper Silurian of Bohemia. 



In the genus PtericMhys (fig. 515) are some very remark- 

 able fishes, first discovered in the Old Pted Sandstone by the 

 late Hugh Miller, and nearly related in most respects to Coc- 



Fig. b\b.—PtericMlnjs cornutiis. Old Red Sandstone. 



costeus. The whole of the head, together with the anterior 

 part of the trunk, was defended by a buckler of large ganoid 

 plates suturally united, those covering the trunk forming a 

 backplate and a breastplate articulated together at the sides. 

 The rest of the body was covered with small ganoid scales. 

 A small dorsal fin, a pair of ventrals, a pair of pectorals, and 

 a heterocercal tail-fin were present. The form of the pectoral 

 fins is the peculiar characteristic of the genus. These were 

 in the form of two long curved spines, somewhat like wings, 

 covered by finely -tuberculated ganoid plates. From their 

 form they cannot have been of much use in swimming ; but 

 they probably, as suggested by Owen, enabled the animal 



