1102 



SCANDINAVIAN FISHES. 



induced by age. Judging hy those species whose de- 

 velopment FiiiES had an opportunity of tracing, he 

 remarised, as a rule ])robably of general application, 

 tliat no species of Ray belonging to tha type with an 

 odd number of rows of caudal a( iilei, wlicn young or 

 newly hatched, lias more tlian one such row, which 

 tiien invariably occupies the median line of the tail. 

 The lateral rows do not appear until the fish has 

 reached a more advanced age. Most of the Scandina- 

 vian species fall under this type, but develop in a di- 

 rection involving something peculiar to and characteristic 

 of each. In some the lateral rows always project from 

 the side-margin of the tail, in others between this mar- 

 gin and the median line. In certain forms the spines 

 of the lateral rows never attain the same size and 

 strength as those of 'the median row, while in others 

 the relations are reversed. In some species the spines 

 of the median rows are persistent even at n very ad- 

 vanced age, in others they are normally lost or shed. 

 The form of the jaw-teeth, remarked Fries, has 

 been rejected as a specific distinction by Cuvier and 

 other writers, and on the whole with good reason, for 

 greater differences of dentition may often be observed 

 between the young and the old, between the male and 

 the female, than can be determined between two nearlv 

 related species. But it is equally certain, he wrote, 

 that most of the species, not to say all the Scandinavian 

 ones, have a fixed form of dentition proper to them, 

 whereby some of them can safely be distinguished, and 

 some — e. g. the Thoridjack, Shagreen Skate, and Starry 

 Ray — are so ^vell marked in this respect that they can 

 be confounded with no other species. To gain a right 

 conception of the dentition of each species, the deve- 

 lopment of the teeth must be carefully followed, and 

 a good clue is afforded to the investigator by a com- 

 parison of the teeth nearest tiie cornei's of the mouth 

 Avith those in the middle of the jaw. The former are 

 arrested, as it wei'e, at a lower grade of development, 

 and most nearly resemble the teeth of the young; the 

 latter exhibit the highest stage in the dental develop- 

 ment of the species. The several intermediate rows 

 between the said points show the transitions from the 

 lowest to the highest development of the teeth. If at- 

 tention be paid to this, and the gradual detrition to 

 which the outermost (foremost) transverse rows in the 

 mouth are subjected l)e also taken into consideration. 



the greater number of the said anomalies in tlie denti- 

 tion of a s[)ecies disappear. As in the preceding fa- 

 mily, the males are characterized by more pointed jaw- 

 teeth than those of the females: but only in one of the 

 species indigenous to Scandinavia (the Thornl)ack) is 

 the dentition of each sex thoroughly distinct: in tlie 

 others the difference is sometimes so slight that it has 

 even been overlooked. 



The form of the snout affords cliaracters of no 

 little importance and constancy, especialh- if tlic alte- 

 rations of growth l)e kept in mind; and the variations 

 in the form of the snout are attended by differences in 

 the general configuration of the body, which form is 

 really determined by that of the snout and the pectoral 

 fins. To find a safe e.xpression for these variations in 

 the form of the snout. Fries compared the length ot 

 two lines, one drawn right across the head through the 

 centre of the pupils, the other at right angles to this 

 and extending to the tip of the snout. The species in 

 which the latter line is less tlian lialf as long as the 

 former, he called blunt-snouted; those in which the 

 length of the snout is more than half or at least half 

 the breadtli of the head at the said point, he ranged 

 among the sharp-snouted Rays (the .Skates). Another 

 expression of this, which besides affords an often re- 

 quisite character from the under surface of the head, 

 may be obtained by comparing the least width between 

 the inner margins of the nostrils (the base of the nasal 

 valvule) with the distance between tlie nostrils and the 

 tip of the snout, whereby we find that in tiie blunt- 

 snouted species the length of the base of the nasal 

 valvule is more, in the sharp-snouted species less, than 

 70 % of tiie distance Iietween the nostrils and the tip 

 of the snout. The form of the snout also supplies an- 

 other charac^ter, wliich was indeed remarked by Fries 

 in his descriptions, but has won greater recognition in 

 more recent times". In the Ravs with a very pointed 

 snout a line drawn from the tip of the snout to the 

 anterior margin of the outer tip of the pectoral fin falls 

 entirely outside the disk, whereas in the blunt-snouted 

 Rays it at least ])arth' cuts tlie same. 



From tiie position of the dorsal fins with relation 

 to each other Nilssox'' deduced a specific character the 

 value of which was also appreciated by Fries. Some 

 species, such as the Starry Ray, have the two dorsal 

 fins set quite close together on the tail ami without 



See E. MoREAU and DOderlein. 

 Prodr. Ichthyol. Scand., p. 119. 



