166 Prof. E. D. Cope on the Systematic Relations of Fishes. 



with an eel-like vertebral column, oris isocercal', it presently, 

 by the upward curvature of the column and uner^ual develop- 

 ment of the caudal fin, becomes di])hyocercalj but ceases to grow 

 before it has quite accomplished this stage. The Polypterus, 

 the Eels, Gymnarclius., and other fishes ossify the vertebrae in 

 the isocercal stage. The heterocercal type is seen in the Chon- 

 drostei, where the vertebrae never ossify. In Lei^idosteus and 

 Amia they ossify in this stage. 



I further specify the characters of the orders of Physostomi 

 and the families they contain in the paper itself. 



Physoclysti. 



The following is an analytic synopsis of the orders. They 

 all have the parietals entirely separated by the supraoccipital, 

 and lack the precoracoid ; the symplectic is present, except in 

 Ostraciunij where it is not ossified. 



A. Scapular arch not suspended from the cranium. 

 Superior branchio-hyals and pharyngeals developed ;• infe- 

 riors and maxillary distinct. 15. Opistlwmi. 



A A. Scapular arch suspended from the cranium. 



1. Ventral fins abdominal. 



Branchial arches well developed, the bones present, except 

 fourth superior pharyngeal ; third much enlarged ; inferior 

 pharyngeals distinct. 16. Percesoces (Mullet &c.). 



Third and fourth superior pharyngeals much enlarged, infe- 

 rior pharyngeals coossified. 17. Synentognatki (Soft Gar), 



Superior branchio-hyals and pharyngeals reduced in num- 

 ber; inferiors separate; interclavicles present. 18. Hemi- 

 hranchii (Pipe-fishes) . 



Superior branchio-hyals and pharyngeals and basal branchio- 

 hyals wanting ; gills tufted. 19. Zo^jAoira^ic/in (Sea-horse).- 



2. Ventral fins thoracic or jugular. 



First vertebra united to cranium by suture ; epiotics united 

 behind supraoccipital ; basal pectoral radial bones elongate. 



20. Pediculati (Goose-fish &c.). 



Posterior cephalic region normal, anterior twisted so as to 

 bring both orbs on one side ; inferior pharyngeals distinct. 



21. Heterosomata (Flounders). 



Cranium normal ; the premaxillaries usually coossified with 

 the maxillaries behind, and the dentary with the articular ; 

 pharyngeal bones distinct. 22. Plectognathi (File-fishes). 



Cranium normal ; bones of the jaw distinct ; inferior pharyn- 

 geal bones distinct. 23. Percomorphi (Perch). 



Cranium normal ; bones of the jaws distinct ; third superior 



