Te leostei — Physos torn i. 



33 



arranged in Table-cases 48-56 and Wall-cases 15-18, and the least 

 specialized are placed first, while the highest and some aberrant 

 forms close the series. 



A B 



Fig. 71.— Scales of Teleostean Fishes. 

 a, Cycloid ; * b, Ctenoid.+ 



Suborder I. — Physostomi. 



The Physostomi are so called from the usual persistence in them Wall-cases, 

 of the duct connecting the air-bladder with the oesophagus (gullet), j™ *' 15 > 16 - 

 which constitutes so conspicuous a feature in the Ganoids and Nog ^ 9 to g 3 

 Dipnoi, in which it helps to form the primitive "lung." They are 

 also characterized, as just remarked, by the abdominal situation 

 of the pelvic fins and the absence of all spinous rays, except the 

 occasional single one in front of the pectorals and dorsal. 



The first family of importance is that of the Salmonidce, which 

 is considered to embrace, among other extinct forms, three genera Table-case 

 from the English Chalk, Osmeroides, Acrognathus, and Aulolepis. n . 49. 

 The two latter are extremely rare, but the former is one of the 

 most characteristic fishes of the period. There is a fine series in 

 the table-case, including the type-specimens, many obtained from 

 the collection of the late Dr. Mantell, and several beautifully 

 worked out of the chalky matrix by this distinguished pioneer in 

 palaeontology. Those of Osmeroides are especially perfect, and, 

 like most fossil fishes from the Chalk, they are almost uncom- 

 pressed, the fine calcareous particles having replaced the muscular 

 and other tissues as rapidly as they were destroyed by decomposition, 

 thus preventing the collapse of the flanks, and preserving the 

 natural rotundity and form of the fish when living. 



Fig. 72.— Capelin (Hallotus villosus) in nodule of Glacial Clay, Greenland. 



Some closely allied fishes from the Eocene Slates of Glaris, 

 Switzerland, and the Miocene of Licata, Sicily, are placed in the 

 genus Osmerns, to which the living " Smelt" belongs. And the 



* Cycloid, circular scales. f Ctenoid, having the margin toothed (comb-like). 



D 



