156 REPORT OF STATE GEOLOGIST. 



short at the base of the caudal. Such tails are, outwardly at least, 

 homocercal. 



The paired fins are usually four in number, two pectorals and two 

 ventrals. The pectorals correspond with the anterior limbs of other 

 vertebrates, the ventrals to the hinder limbs. In the lower fishes (cat- 

 fishes, suckers) the ventrals are placed considerably behind the pectorals, 

 that is, they are abdomhicd In other forms, as in the bass, the ventrals are 

 brought forward close to, and even immediately under, the [)ectorals. In 

 such cases the ventrals are said to be thoracic. In a few species, as the ling 

 {Lota), the ventrals are located even in front of the pectorals, and are 

 then said to he jugular. The number of rays in the ventrals furnishes a 

 useful character in the classification of the fishes. In many of the higher 

 families of fishes the front of the ventral is occupied by a spine, and 

 this is followed by five soft rays. In some families the spine is missing, 

 while the number of soft rays is increased or diminished. The ventrals, 

 and occasionally even the pectorals, may be entirely wanting. The 

 pectorals are always placed immediately behind the head. The upper 

 rays are the strongest. In the cat-fishes the anterior ray is a stout 

 serrated spine. In the lower families of fi^ihes the pectorals are inserted 

 below the axis of the body; in the higher families they are usually 

 placed higher up 



Some of the modifications of the alimentary canal may be briefly no- 

 ticed. The stomach is sometimes little, if any, larger than the remainder 

 of the canal. In some species it is bent like a horseshoe, and is then said 

 to be siphonal. In other fishes, as our white fishes, the stomach forms a 

 blind sac, the gullet entering at the same eud as that from which the 

 small intestine departs. The term c(ecal is applied to such stomachs. 

 Into the beginning of the small intestine are often found opening a num- 

 ber of blind tubes, the pyloric cfeca. The intestine terminates-usually in 

 front of the anal fin. In the pirate perch, however, the vent is situated 

 in front of the ventral fins, just below the preopercle. The class which 

 is composed of the bony fishes may be defined as follows : 



Vertebrates breathing by means of gills, furnished with rayed fins and 

 having the primitively cartilaginous skeleton supplf-raented by membrane 

 bones. 



Limbs, if present, one or two pairs; not termiuatiug in recognizable 

 digits. Median fins supported by rays. Shoulder girdle strengthened 

 by a membrane bone, the clavicle. Brain-case, organs of sense, and the 

 jaws, provided with membrane bones. Gill cavity enclosed by an oper- 

 culum, which contains one or more membrane bones. Gills free along 

 their outer border. Blood cold. 



