BONY FISHES AND GANOIDS. 509 



may be mentioned the vendace (C. vandesius), the pollan (C. pottaii), 

 and the powan (C. dupeoides), all of which are British. Like smelts, these fish 

 have small eggs ; but then they have a great number of blind appendages to 

 the intestine, and if any teeth remain in the adult, they are usually restricted 

 to the tongue, while even in the young state these organs are minute. The 

 cleft of the mouth is always much less deep than in the Salmo, while the 

 forking of the tail is more strongly marked. In common with the grayling, 

 these fishes differ from the other members of the family in that the two 

 parietal bones meet together for a short distance in the middle line in ad- 

 vance of the supraoccipital. The genus extends over a considerable portion 

 of Northern Europe, Asia, and America ; and its very numerous members 

 are for the most part permanent inhabitants of fresh water. The grayling 

 (Thymallus), which have a geographical distribution very similar to that of 

 Coregonus, differ from that genus by the taller and longer dorsal fin, in which 

 the number of rays varies from thirteen to twenty-three. The mouth, too, 

 has a smaller cleft ; while the blind appendages of the intestine are much 

 less numerous, and teeth are present in the jaws, and on the palatines and 

 the head of the vomer, although wanting from the tongue. Although rang- 

 ing from Lapland to Venice, and from England to Russia, the grayling is a 

 very local fish, which is unknown in Ireland ; and it appears that only under 

 certain conditions will it thrive and multiply in a river. A writer in Land 

 and Water for 1868 remarks, that "there is one singular peculiarity about 

 the grayling that distinguishes it from all other .species of Salmonidce, and 

 that is its remarkable odour. It resembles more than anything else the smell 

 of a freshly-cut cucumber ; by this criterion it may be immediately detected. 

 Some authorities assert that the smell of this fish resembles thyme, but I 

 cannot endorse this, or perceive the slightest affinity." 



A small family is represented by the North American fresh-water Percopsis 

 gnttata and the allied Columbia transmontana, which, although possessing the 

 structural features of the Salmonidce, assimilate in the nature 

 of the scales and the bones of the mouth to the perch Percopsidse. 

 tribe. 



SUB-ORDER VI. ^THEOSPONDYLI. 



This and the next subordinal group of the Actinopterygii are now respec- 

 tively represented only by a single North American genus, although both 

 were abundant during earlier epochs of 

 the earth's history. To understand 

 fully their relationship to other fishes 

 it is essential to take the extinct forms 

 into consideration, but as this is im- 

 possible here, their general structural 



features can be only very slightly touched j^ 32. BOXY PIKE. 



upon. The present sub-order is now 



represented only by the three species of bony pike (Lepidosteus) from 

 the fresh waters of North America, which typify the family Lepidosteidm. 

 These fishes, some of which measure fully six feet in length, have the 

 head covered with bony plates, and the whole body invested with a 

 coat of hard, shining, quadrangular scales, which articulate together by means 

 of a peg and socket. The long head is depressed, with the jaws well-armed 

 with teeth ; and the body is elongated, with the anal and dorsal fins which 

 have no spines placed near the tail, and the latter of the so-called abbreviate 



