452 



CONTRIBUTION TO THE 



Similar to the last, but with interoperele and maxillary bones, and osseous brancliiliyals. 



2 QLAHIOSTOMI. 



The first order embraces the single family of Spatularidis, the second, that of the Aecipenseridas. In both, the 

 chorda dorsalis persists, the tail is hoterocercal and the osseous cranium is little developed. The basal and radial 

 elements of the limbs, with the coracoids, are not ossified. 



Physostomt. 

 The following key will express the leading features of the orders of this division. 



I A pracoracoid arch . 

 A A coronoid bone. 

 Maxillary in many pieces ; vertebrae opisthocoeltan. 3 ginglymodi. 



Maxillary not transversely divided ; vertebral amphicoelian. 4 halkcomokphi. 



AA No coronoid bone. 

 * No symploctio bone. 

 Pterotic simple, anterior vertebra with ossicula auditus; supraoccipital and parietals co-ossifiod. 



5 NEMATOGNATHI. 



Pterotic annular, including a cavity closed by a special bono ; parietals distinct, vertebras simple. 



6 SCYPHOPHOEt. 

 * * Symplcctic present. 

 Anterior vertebra co-ossified and with ossicula auditus. 

 Anterior vertebras similar distinct, without ossicula auditus ; 



II. No pnecoracoid arch. 

 A Scapular arch suspended to cranium. 



* A symplcctic. 



Pterotic and anterior vertebras simple ; parietals separated by supra-occipital. 

 Anterior vertebras modified; parietals united ; pectoral fins. 



* * No symplcctic. 

 Anterior vertebras simple ; a prseoperculum and maxillary ; no pectoral fins. 



A A Scapular arch free behind the cranium. 



* A prcoperculum. 



A symploctic ; maxillary well developed ; no pectoral fins. 

 No symplcctic ; maxillary lost or connate ; pectoral lins. 



* * Preoperculum wanting or rudimontal. 

 No syniplectic, maxillary, nor pectoral fins ; no pterygoid. 

 Of the above orders, the Ilaplomi (pike, etc.,) approach nearest the Physoclysti of the families OpheocepMlidw 



and Atheriividai ; and the IMostomi of the family Symbranclrida, to the Physoclyst family of MaUaccmbelidce. The 

 affinities between these families is, in both cases, so close as to render the distinction of the primary divisions in 

 question hardly worth preserving. 



The complete development of the support of the caudal fin is seen in many members of this tribe, while in many 

 of them it remains in its primitive condition. Among I'hysoclysti it is nearly always complete, though in a few 

 {Trichiuridm, etc.,) it remains larval. 



In the first development of the vertebra] column in fishes, it forms a straight axis. The fin is represented by a 

 fold of the integument, which extends equally round its extremity. In this membrane the rays are developed, and 

 in many fishes they remain thus equally distributed. In this case, the caudal vertebrae remain in a straight lino 

 to the extremity, and we have a termination such as is seen in Lepidosiren and the eels. This form of tail may be 

 called the isocercal. 



If now, the radii, basal or distal acquire a greater development on the lower side of the cud of the column, thoso 



7 PTjBCTOSPONDYtl. 



8 ISOSPONDYM. 



9 UArLOMI. 



10 GLANENCTIEU. 



11 ICHTIIYOCKl'Jir.r. 



IS IIOLOSTOMI. 



13 ENCIIE1YCEPHALI. 



14 COLOCEITIALI. 



' 



