CHARACTERS OF THE PLECTOGNATHES. 19 1 



cartilaginous^ or that they take a long time to harden; 

 and thatj in all, ^^ very small vestiges of ribs are to be 

 found." The third is an equally important character:- 

 the operculum and branchia_, indeed^ exist; but in a very 

 imperfectly developed state, when we compare them 

 with those of ordinary fishes ; and they are altogether 

 concealed by being covered with the thick skin of the 

 body, which only leaves a small cleft, or spiracle, by 

 which the water taken into the mouth escapes. Hence 

 they breathe, like the Cartilagines and the apodal order, 

 by spiracles. The other characters of the group are 

 secondary, because they serve more to determine the 

 family divisions, than to characterise the entire order. 

 In the Balistid(B, or tortoise-fishes, the maxillary bone 

 is soldered to the intermaxillary, which alone form.s the 

 jaws, and to which the palatine arch is united by a 

 suture with the skull, so that it possesses no power of 

 motion ; the mouth is thus most imperfect, and is 

 always very small. In another typical group, the eyes 

 are also very small, but are placed almost vertically : the 

 pectoral fins are very large, and often have some re- 

 semblance to feet, being placed on a sort of peduncle, 

 which enables these frog- fish to crawl upon the ground : 

 the mouth opens upwards, and the lower jaw is longest. 

 In one group only — the most aberrant of all — is there 

 a variation in the branchia, indicating an affinity to the 

 class of animals which next succeed, namely, the Am- 

 phibia. 



(168.) Thus characterised, as a whole, the Plecto- 

 gnatlies appear to arrange themselves into the following 

 natural families : — 1 . The Balistidce, or cheloniform fishes, 

 having the body oval or round, and almost always 

 covered with osseous plates or armed with prickles : 



2. The ChironectidcB, or frog-fishes, where the pectoral 

 and ventral fins, particularly the former, assume the 

 appearance of feet ; the body being thick and smooth ; 



3. The Lophidce, having the head enormously large and 

 greatly depressed : and, 4. The SygnathidtT, of a long 

 serpent-like shape, covered with hard plates, and the 



