354 



SYNOPSIS OF TJIE CYPRINID/E OF PENNSYLVANIA. 



nearly allied, Chondrostoma and Rhodeus, possess intestinal canals 2.06 and 3.5 times the 

 length of the body respectively. 



The alimentary canal in the Cyprinida: offers no distinction into stomach and small and 

 large intestine ; its anterior portion is generally of greater diameter than that succeeding. 

 The principle of its arrangement is that of a sigmoid with the three limbs apprcsscd and 

 in contact. In those genera with short intestines, the proximal flexure is anterior to the 

 hinder extremity of the abdominal cavity, the distal, behind the anterior, thus reducing 

 the median tract. Length is gained by extending the proximal flexure to near the vent 

 and the anterior to near the head ; while the additional complications of more vegetable- 

 feeders take place first about the distal or anterior flexure, where portions of the middle 

 and distal tracts may be together several times laterally folded, or new flexures may be 

 added in the middle and distal tracts themselves. By the last mode, accommodation for 

 the greatest extent is procured. In any case the proximal tract is not flexed, evidently 

 that it may serve as a receptacle for the objects taken as food. The liver is attached to 

 two, or sometimes three tracts, in a band or bands between them. 



The Cyprinidue of the Eastern district of North America appear to be referable to four 

 tribes, as follows: 



Dentary bones straight and flat, united together throughout their length; natatory bladder lying along the 

 vertebral column, above the alimentary canal ; opercular and mandibular bones not cavernous. COOHLOBOEI. 



Dentary bones slender, arched, and widely separated, except at their symphysis ; natatory bladder lying along 

 the vertebral column, and above the alimentary canal; opercular and mandibular bones with external cavernous 

 chambers. OffiLOPHORI. 



Dentary bones slender, arched, widely separated, except at their symphysis; natatory bladder lying along the 

 vertebral column, and above the alimentary canal ; opercular and mandibular bones without external cavernous 

 chambers. Ei'JCYSTi. 



Dentary bones slender, arched, widely separated, except at their symphysis; natatory bladder suspended in the 

 centre of the abdominal cavity by numerous convolutions of the alimentary canal which surround it ; opercular 

 and mandibular bones without external cavernous chambers. MESOOYSTI. 



The genera are as follows : 



Tribe I. COCIILOBOJtI. 



Barbels none. Premaxillaries not projectile ; skin of lip and front continuous. Teeth 1, 4 — 4, 1 or 2, hooked, 

 without masticatory surface. Dorsal tin above ventrals ; anal basis short. Mouth inferior; mandible much con- 

 tracted, with lobe on each side of base. exoolossum. 



