DESCRIPTIVE TEEMS. 761 



10. Vpper pharyngeals, two sets of bones, nsnally rounded, placed on the upper side of 

 the oesophagus, iehind the gill arches. 



11. Lower pharyngeals, one on each side of the median line, helow the cesophagus, and 

 ieMnd the gill arches. These bones are modified gill arches, and their forms vary much 

 with the different suborders of fishes, and their structure is of great importance in the 

 system of classification. In the Black Bass they are flattish and somewhat triangular ; 

 in the Sucker they are sickle-shaped. 



The comparative size of the liead is described by noticing how many times its length 

 (along the side, from the snout to the posterior edge of the opercle), is contained in the 

 length of the tody (measured along the side from the tip of the snout to the middle of the 

 base of the caudal fin). Thus " head 4J in length" (as is the case in the Sucker) in- 

 indicates that the length of the head is a little less than one-fourth that of the head 

 and the body. The length of the head is proportionately rather greater in young fishes 

 than in adults. 



Below the subopercle and interopercle, and nearly parallel with them are the bony 

 iranehiostegal rays enveloped in the gill membranes. These are three in number on each 

 side in the Sucker, six in number in the Black Bass, and their number often furnishes 

 important characters.* 



The scales when normally developed, are either Ctenoid (with the exposed or posterior 

 edge rough or ciliated as in the Perch or Black Bass), or Cycloid (smooth as in the Sucker). 

 In most cases, there is a series of scales along each side, each of which is provided with 

 a mucous tube, these forming a conspicuous raised line known as the lateral line. In 

 many scaleless fishes this chain of mucous tubes is developed. 



The relative size of the scales is indicated by counting them- Of course, the smaller 

 they are proportionately, the more numerous they are. Tlie numter forming the lateral line 

 is oneofihe mostvaluaile and constant of specific characters, being subject to but slight varia- 

 tions. " Scales 10-65-7," the formula ef our Sucker, signifies ten series of scales between 

 the dorsal fin and the lateral line ; 65 scales in the lateral line, and seven series between 

 the lateral line and the ventrals. 



The fins are (a) the paired fins, which are the pectorals (corresponding to the anterior 

 limbs or arms) situated immediately behind the gill openihgs, and the ventrals (corres- 

 ponding to the posterior limbs) placed either behind or below the pectorals ; and (6) 

 the vertical fins, or fins on the median line of the body. These are the dorsal (on the 

 back), caudal (on the end of the tail), and the anal (on the lower side, J)ehind the vent). 



The dorsal is sometimes divided into two fins, in which case the anterior is called 

 first dorsal, the posterior, second dorsal. 



The position of the fins is a matter of much importance. The ventrals are said to be 

 ahdominal when they are inserted on the belly, notably iehind the pectorals, as in the 

 Sucker, thoracic when inserted under the pectorals or close behind them, as in the Black 

 Bass, jugular when in advance of the pectorals, as in the Cod fish. 



The rays of which the fins are composed may be either spines or soft rays. 



The spines are usually stiff and pointed, and are never jointed or articulated, and are 

 never branched. In those fishes which have spines there is commonly one in each ven- 

 tral fin, none in the pectoral or caudal fins, one or more in the front part of the anal fin 

 and several in the anterior part of the dorsal fin, constituting the whole first dorsal 

 when there are two dorsal fins. 



The soft rays are always articulated or jointed towards their tips, and most of them 

 are also branched. They are therefore usually wider at their tips than at their bases, 

 and are seldom rigid, unless rendered so by drying. In all cases where the dorsal and 



