464 PISCES SUB-CLASS III.TELEOSTOMI. 



Of far more general interest are the twelve genera constituting the family 



Percidce, in all of which there are never more than two spines in the anal 



tin, while there are two pairs of external nostrils. Like their 



Family nearest allies, the perches generally have a complete lateral 



Percidce. line, no scales on the median fins or barbels to the mouth, 



and the teeth conical. Six to eight pairs of branchiostegal 



rays are present, as well as four pairs of gills, the last of which is followed by 



a slit ; and the rayed portion of the dorsal fin does not much exceed the anal 



in length. Although Lucioperca (Stizo- 

 stedion) and Percarina enter salt water, 

 the family is essentially a fresh-water 

 type, its members being spread over 

 North America, Western Asia, and 

 Europe. Among the generic types of 

 the family are the true perches (Perca), 

 with a distribution equivalent to that 

 of the family ; the aforesaid Lucio- 

 perca, or pike-perches, with a similar 



Fig. 4. COMMON PERCH. range ; the three small species of the 



Danubian genus Aspro ; Percarina, with 



two species from the neighbourhood of the Sea of Azov and the Black Sea ; 

 and the ruffes (Acerina), of which the three representatives are restricted to 

 Europe and Asia. 



Nearly allied to the last is the family of Serranida, or sea-perches, dis- 

 tinguished by the development of an internal lamina from the second sub- 

 orbital bone supporting the globe of the eye, the number of 

 Family spines in the anal fin being variable. In this extensive 



Serranidce. family the genus Centrogenys is noteworthy, on account of 

 the union of the lower pharyngeal bones. It would be 

 tedious to mention the distinctive characters of even the commoner and best 

 known genera, and only a few will be referred to at all. As an example of 

 the group of the sub-family Serraninw, with two dorsal fins, we may take the 

 South American Percichthys, which is one of the few fresh-water types. In 

 this and four other allied genera the tongue is smooth, but in the bass, 

 Morone, which have likewise two dorsals, that organ is covered with patches 

 of teeth. Whereas some bass are marine, others are fresh- water in habitat. 

 They all have nine dorsal and (like the other members of the sub-family) 

 three anal spines. Among the group with a single dorsal fin, especial interest 

 attaches to the widely-spread sea-perches of the genus Serramts, on account 

 of the vast number of species and the large bodily size to which some of them 

 attain. Although the tongue is edentulous, teeth are developed on the 

 palate, and large tusks occur at intervals among the small teeth in the 

 margins of the jaws. Centropristes is an allied genus. In another group of 

 the same sub-family Mr. Boulenger includes the genera Plesiops and 

 Trachinops, which were formerly referred to the Nandidce. In these the 

 lateral line is double, consisting of an upper portion, which disappears pos- 

 teriorly, and a lower running along the middle of the side of the tail. 

 Whereas the first genus is from the coral-reefs of the Indo-Pacific, the second 

 is Australian, both being marine. To another sub-family Centropominai 

 distinguished by the extension of the lateral line on to the caudal fin, 

 belong the two species of Lutes, one of which is Nilotic, while the other 

 is Oriental and Australian. The Oriental species grows to a length of 



