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Inner scries 5-5. 



Chrosomus. 



SYNOPSIS OF THE CYPRINIDiE OF PENNSYLVANIA. 



5-4. 

 Phoxinus. 



Chrosomus. 



359 



ChonJrostoma. 



4-4. 



Ilybognathus. 

 Ilyborhynchus. 

 Piinephales. 

 Campostoma, 



EXOGLOSSUM, Rafinesque. 

 Journ. Acad. Nat. Sci., Phila., I, 1818, 420. 



D. Os dcntale. 

 Ar. Articulare. 

 An. Angulare. 

 Ft. Pterygoideum. 

 Qu. Quadratum. 

 J. O. I nteroperculare. 

 P. O. Prceoperoulare. 

 S. 0. Suboperculare. 



O. fly. Os glossohyoideum. 

 />. 11;/. Basihyoideuta. 

 C. Hy. Ceratohyoideum. 

 U. fly. Urohyoideum. 

 3 Br. Had. Branchiostegi. 

 CI. Claviculus. 

 M. Mass. Muse. Masseter. 



This genus was first properly defined by Professor Agassiz in his excellent review of 

 the genera of American CyprinidfE, in 1855, though lie only explained the singular ar- 

 rangement of the dentary bones by calling it " a projection of the symphysis of the 

 branches" of the jaw, nor regarded its peculiarity as of so much weight as here indicated. 

 Hence he placed it as affined to Campostoma. Girard, in his more extensive review 

 (1856), correctly denies this relationship, and places it among the more ordinary types, — 

 as Alburnus, &c. This approximation appears to me as erroneous as the last ; in nature 

 it has much of the manners of the Campostoma?, but not their habits, and the structure of 

 the mandibular arch has no parallel among either series. I have therefore established for 

 it a distinct tribe. 



The scries of pharyngeal teeth is situated chiefly on the inferior limb of the bone, the 

 lower tooth being on a line with the angle of the lateral ala. The arched bones them- 

 selves are unusually small, and situated more within the scapular arch than in other 

 genera. 



The mandible is not margined by lips, nor covered with a cartilaginous sheath ; the 

 basal lobes are the rudiment of the former. The incompletely defined body which in this 

 family represents the tongue is situated in the back part of the oral cavity, since the glos- 

 sohyal bone is excluded from its usual place, and is short ; its approximation to the intro- 



