SYNOPSIS OF THE CYl'KINlDiE OF PENNSYLVANIA. 



397 





The carp is olivaceous, the gold fish varies from olivaceous to black, silvery, and crim- 

 son. Both are taken in the Schuylkill, the Carassius much the more abundantly, as I 

 have witnessed, as far as Conshohocken, sixteen miles above Philadelphia ; the latter fish 

 occurs no doubt much higher up this river. 



The crania of these, and of all other genera of Cyprinidae, in individuals of all ages, I 

 have found to be fully developed, while among Catostomidae, as Catostomus (IL/lomyzon 

 and Plychoatomus) and Carpiodes, its superior wall is interrupted by a longitudinal fonta- 

 nelle. In the genus Cycleptus, however, the cranium is as complete as in the Cyprinidas. 

 It may also be observed as characteristic of the two families, that in the latter the masti- 

 catory table of the basi-occipital occupies only the basal portion of the basi-occipital ensi- 

 form process, while in Catostomus the latter is entirely covered by a broad cordiform 

 table, winch is largely lacunary and not solid. 



The characters of our genera of Epicysti, having been already given, their serial affin- 

 ities may be usefully presented in the following form : 



Pcleous. 

 i 



Alburnus. Aspius. 



i i 



Gobio. Alburnellus. Olinostomus. 



i i i 



Semotilus. Argyreus. Phoxinus. 



i i i 



Ceratichtbys. Photogenis. 



i i 



Hybopsis. 

 i i i 

 Hyborhynchus. • Hypsilepis. Stilba. 



■ i ii 



Pimephales. Ooohlognathus, Chrosomus. 



■ 



Hybognathus. 

 i 

 Chondrostoma. 



In connection with future study of this and other types of organized beings, the follow- 

 ing observations on the probable law of evolution of types are appended. 



In the present state of our knowledge, we believe the following laws can be established : 



I. That genera form series indicated by successional differences of structural character, 

 so that one extreme of such series is very different from the other, by the regular addition 

 or subtraction of characters, step by step* 



II. That one extreme of such series is a more generalized type, nearly approaching in 

 characters the corresponding extreme of other series. 



* St. Hilaire, Owen, Aaasaiz. 



