Class 2. Pisces. Order 5. Teleostei. 389 



vulgaris) in fresh water, has a short anterior, and a long posterior dorsal fin 

 (the latter corresponds to the two dorsal fins of Gradus) ; an anal fin, and one 

 barbule. To an allied family (0 p h i d i i d eb) belong the Sand-eels {A-mmo- 

 dytes), small and elongate with no mandibular teeth ; with projecting lower 

 jaw : without pelvic fins ; with long dorsal and anal fins ; on the coasts of 

 Britain. To the same family belongs also the genus Fierasfer, the species of 

 which take up their abode in the cloaca of Holothurians (without being actually 

 parasitic, since they feed upon small animals) : an allied genus, Bnchelyophis, 

 is a true parasite. 



3. Flatfish (Flev/roneatidx). The body is a laterally compressed disc; 

 both eyes on the same side, in some species on the right, in others on the left 

 (in a few species, some individuals have the eyes on the right, others on the 

 left) ; the blind side is white and turned downwards, the other colouj-ed ; the 

 mouth is often somewhat asymmetrical, being larger on the blind side where 

 the premaxilla and maxilla are better developed ; dorsal and anal fins very long, 

 anus far forwards ; pelvic fins in front of the pectorals ; no spinose rays. The 

 larvse are perfectly symmetrical, with the eyes on either side of the body, and 

 the animal swims with the ventral surface downwards ; later, one eye moves 

 round to the other side, and the animal lies upon one side. Amongst the 

 forms inhabiting British seas are : the Plaice (Plevjroneetes platessa), eyes right 

 (vei-y rarely left) ; scales smooth : the Dab (PI. Umanda), eyes right ; scales 

 rough: the Flounder (PZ. Resits), with rough bony knobs ; eyes usually right 

 but frequently left ; it occurs not only in the sea, but also in fresh water : 

 the Sole (Solea vulgaris) disc not so wide as the foregoing; eyes right; the 

 Halibut (Hippoglossus vulgaris), also with eyes on the right, attains a con- 

 siderable length (2 m.) : the Turbot {Bhombus maximus), with bony warts, and 

 the Brill (iJfe. Ixvis) with small smooth scales, both with the eyes on the left side. 



4. The Perch family (Percidx). Scales ctenoid; two dorsal fins, 

 which are generally, however, united, the anterior with only spinose rays ; pelvic 

 fins below the pectorals ; operculum with spines. To this family belong the 

 Common Perch {Perca fluviatilis), and the Pope (Acerina cernua) with 

 fused dorsal fins. Both are freshwater, the former occun-ing also in brackish 

 water, and are found in England. To an allied family belongs the Climbing 

 Perch (Anahas) mentioned before (p. 375). 



6. The Wrasses [Labridx) recall the Pei-oh in their external appear- 

 ance, but are distinguished by the fusion of the lower phai-yngeal bones, and 

 especially by a pad-like thickening of skin (the lip) along the edge of the 

 mouth. To this family, which is represented by several small species in the 

 North Sea belongs the Parrot-fish [Scarus) ; in this form the edge and 

 a portion of the front of the premaxilla and maxilla, are beset with teeth 

 which are coimected with each other, and with the rest of the jaw by means of 

 a bony mass, so that a continuous cutting edge is formed. Grinding teeth, 

 united in the same way, occur on the superior and inferior pharyngeals. The 

 Parrot-fish, which belong exclusively to warm seas (one species in the 

 Mediteri'anean), can bite through even branches of Coral. 



6. "Peter's Thumb" (Trachinus draco) is a somewhat elongate form 

 with a short head and small cycloid scales ; with two dorsal fins, the posterior 

 being long and possessing soft fin-rays, the anterior quite short and with spinose 

 rays ; pelvic fins in front of pectorals. On the operculum is a bony spine, with 

 two poison glands, lying in grooves on its sm-f ace, and opening at its tip ; 

 similar glands in the spiny rays of the dorsal fins.* Abundant in the North 

 Sea; usually seen with the larger part of the body buried in the sand. 



* Similar poison organs ooour also in a few other tropical Fish. 



