THE GANOIDEI. 1-13 



plates in Polypterus, wMchmay possibly represent branchio- 

 stegal rays. 



In Accipenser, Spaiularia, and Amia, the pectoral arch 

 presents two constituents : one, internal and cartilaginous, 

 answers to tlie cartilaginous pectoral arch of the Elasmo- 

 branchii, and to the scapula and coracoid of the higher 

 Vertebrata ; the other, external, consists of membrane bones 

 representing the clavicular, supra-clavicular, and post- 

 clavicular bones of the Teleostei. In Lepidosteus one centre 

 of ossification appears in the cartilage ; in Polypterus. 

 two. The upper represents the scapula, and the lower the 

 coracoid. 



It has been already stated (p. 39) that Pohjpterus comes 

 nearest to the Elasmobranchii in the structure of the rest 

 of the limb. The numerous dermal fin-rays, all nearly 

 equal in size, are connected with the rounded periphery of 

 the broad and elongated disc formed by the skeleton of the 

 fin ; and the scaly integument is continued to the bases of 

 the fin-rays, which thus seem to fringe a lobe of the integu- 

 ment. Hence the fin is said to be lobate. In the other genera, 

 only two of the basal cartilages are present, and some of the 

 radialia come into contact with the shoulder-girdle between 

 them. la addition, the anterior dermal fin-ray is much 

 larger than the others, and becomes directly connected with 

 the anterior basal cartilage. Thus, in the structure of their 

 fins, as in so many other characters, the Ganoidei are inter- 

 mediate between the Elamnohranchii and the Teleostei. 



In certain Ganoids, as Lepidosteus, Accipensei\ and many 

 fossil genera, the anterior margins of the anterior fin-rays 

 of the dorsal fins, bear a single or a double series of small 

 scales, or spines, called /wZcra. 



In Accipenser and Polypterus, spiracula, or openings which 

 communicate with the mouth, lie on the top of the head, in 

 front of the suspensorium, as in many Elasmobranchs. 



Lepidosteus, Accipenser, and ScapirhyncMis, have branchiae 

 attached to the hyoidean arch, as in the Elasmobranchii. 

 They are now called opercular gills. 



In Polypterus the air-bladder is double and sacculated. 



