SEA TROUT— SALMON-TROUT RACK. 165 



young. Interorbital space convex, and equal to about the length of the snout. 

 Daring the breeding season a knob generally exists at the uj)per side of tho 

 anterior end of the lower jaw in the males. The posterior extremity of the ujipcv 

 jaw reaches to beyond the hind edge of tho eye in full-grown examples, and it is 

 stronger in some varieties than in others.* The foi-m of the gill-coverst in this 

 fish has been held to almost denote species with some authors, to be dependant on 

 sex according to others, or to be of no signification at all. In some the posterior 

 edge of the preopercle is somewhat sinuous, while it has a distinct lower limb ; 

 however, every intermediate form may be found between it and examples in 

 which there is scarcely any trace of a lower limb, or they may even differ on tho 

 opposite sides of the head in the same specimen.;]: The posterior edge of tho 

 opercle and subopercle form a semi-circle, in which the subopercle generally, but 

 not invariably, forms the most prominent point. Several raised and curved lines 

 are mostly present upon the outer edge of the subopercle and opercle. Tecth^ — 

 in the young similar to those in the salmon fry : there is a double row along tho 

 body of the vomer, and a transverse row across the hind edge of the head of that 

 bone. At an early age these vomerine teeth become lost, more quickly in some 

 examples than in others, but generally along the body of this bone there is only a 

 single row in examples a foot or upwards in length : and these have their points 



* This has been denied by Dr. Giinthcr, who, however, gives proofs of its being so in 

 nature. In 1866, in the Catal. of Fish. Brit. Mas., vi, p. 28, he asserted of the Saliiio initta, 

 when criticizing one point of Nilsson's description wherein this author had observed that the 

 maxillary bone extended to behind the eye, that "this is the case in very old males only:" at 

 p. 30, he described a male twenty inches long, stating the maxillary " extends considerably 

 beyond the vertical from the posterior margin of the orbit." Also of a female, 27:} in. long, 

 that this bone " extends beyond the posterior margin of the orbit " (\). 31) ; and of a male, 18^ in. 

 long, wherein this bone "extends considerably behind the vertical from the posterior margin of 

 the eye " (p. 33). 



t I have already (p. 152 ante) referred to Yarrell's definition of the gill-covers and given copies 

 of his figures, while Dr. Giinther (1866) observed that the former author generally termed females 

 with shorter heads as S. trutta and males as S. criox {camhricus). He believed the maxillary bone 

 in the latter to be much stronger than in the former. 



% The following are the proportions observed in a pair of salmon-trout from the Teith, which 

 were used for artificial propagation in November, 1886. Male — 20 in. long, with a well-developed 

 hook to the lower jaw {see fig. 28), 47 cffical appendages, and two teeth in the hind margin of the 

 head of the vomer and three along its body [gee fig. 29, No. 3). Length of head 4i, of pectoral fin 8, 

 of ventral fin 10, height of body ^\ in the total length. Eyes — diameter 6 in the length of the 

 head, 2^ diameters from the end of the snout, and 3 apart. Female — 12-8 in. long, 50 cacal 

 appendages, and two teeth on the hind margin of the head of the vomer and none along its body. 

 Length of head 5, of i^ectoral fin 7^, of ventral fin 8§, height of body 6 in the total length. Eyes 

 — diameter 5^ in the length of the head, IJ diameters from the end of the snout, and 2^ apart. 



§ Jenyns, 1835, observed of S. trutta, teeth " on the vomer extending all along the ridge of the 

 palate." Yarrell, 1836, gave the following formula from which to select. In Salmo erlox 

 {camhricus) the teeth on the vomer occupy in the adult the most anterior part only, and are 

 two or three in number, while in ,S'. trutta they extend along a great part of its length. Parnell, 

 1838, remarked that the number of vomerine teeth, when the hsh has attained about eighteen 

 inches in length, are uncertain, varying from three to nine; nor is it possible to distinguish 

 S. trutta by the teeth only, from some of the varieties of S. erlox {camhricus), at least not before 

 the fish has reached the length of twenty inches, when it will be found that S. trutta has retained 

 from seven to nine of these teeth, and that S. erlox {camhricus) and varieties have lost all except 

 a few, and those confined to its anterior extremity. Dr. Giinther, 1866, asserted of Salmo 

 trutta, '' heai of the vomer triangular, as broad as long, toothless: body of this bone with 

 a longitudinal ridge, armed with a single series of teeth, some of which are bent outwards : the 

 greater part of these teeth are lost at various ages, so that sometimes only three or four are left 

 in specimens twelve inches long, whilst others, much older examples of twenty inches, sometimes 

 show six or eight ; generally only the two or three anterior ones are found in examples of more 

 than twenty inches in length" {Catal. vi, p. 2-4). And at p. 30 when describing a male twenty 

 inches long he remarked that " the body of the vomer has lost all its teeth, and only three 

 remain, forming the transverse series across the posterior part of the head of this bone." Also 

 at p. 33, of a male eighteen and a half inches long, that " all the teeth of the vomer are lost, 

 except three, which occupy the hinder part of the head of this bono." Of the sewin .S'. cam- 

 hricus (or erlox of Yarrell), he observed, "Head of the vomer triangular, broader than long, 

 toothless in adult examples, and armed with a few teeth across its hinder margin in young ones : 

 body of the bone with a sharp longitudinal ridge, in the sides of which the teeth are inserted, 

 forming a single series, and alternately pointing towards the right and left ; in pure (non-hybrid) 

 specimens, these teeth are lost in the grilse state, so that only the two or three anterior remain 

 in specimens more than twelve or thirteen inches long " (1. c. p. 35). 



