32 



Fossil Fishes, 



Order VI.— TELEOSTEI. 



As already remarked, there are among the fishes of the Jurassic 

 period, and especially the later portion of it, several genera having 

 a remarkably Teleostean facies, so far as can be judged from their 

 skeletal parts ; and it is not unlikely that some of these might 

 be correctly placed in this order. Unfortunately, however, the 

 Teleostei mainly differ from the Ganoids in the structure of certain 

 soft parts, — e.g. in the bulbus arteriosus of the heart being non- 

 contractile, the intestine having no spiral valve, and the optic 

 nerves decussating, — and the palaeontologist is thus unable to 

 recognize with certainty any members of the order that have not 

 an obvious and intimate relationship to some known type still 

 surviving. 



Fig. 70.— Skeleton of the Common Perch. 



a, premaxillary bone; 6, maxillary bone; c, lower jaw; d, palatine arch; e, cranium; 

 /, interoperculum; g g', vertebral column ; A, pectoral fin ; i, pelvic fin ; A, spinous 

 dorsal fin ; /, soft dorsal fin ; m, anal fin ; n, upper, and »', lower lobe of caudal fin. 



[The pectoral and pelvic fins each form a pair, and correspond respectively to the anterior 

 and posterior pairs of limbs of the higher Vertebrata. The dorsal, caudal, and anal fins are 

 median and unpaired.] 



For this reason the Teleostei are usually regarded as having their 

 first representatives in strata of Cretaceous age, and here are dis- 

 covered numerous forms allied both to the highest and lowest 

 divisions of the group. There are Acanthopterygian (spiny-finned) 

 fishes, in which a certain number of the anterior rays of the dorsal, 

 anal, and pelvic fins, have already become stiffened into spines, and 

 in which the pelvic fins have mostly advanced forwards to be 

 placed beneath the pectorals ; and there are also innumerable 

 examples of the more primitive division of the order, the Physo- 

 stomi, which have so far retained the characters of their Ganoid 

 ancestry as to possess abdominal pelvic fins, few or no spinous rays, 

 and the margin of the upper jaw very frequently formed in part 

 both by the maxilla and the premaxilla. 



Thus restricted, the fossil representatives of the Teleostei are 



