1106 



SCAXDIXAVIAN FISHES. 



These lateral rows do not ofcujjy the extreme side- 

 margin of the tail, but the space between this and the 

 median series, except where there are two lateral rows 

 on each side, in which case the outer row projects from 

 the said margin. They do not extend throughout the 

 length of the tail, but only a short distance along it; they 

 are not symmetrical, ;ind contain an cxti'emcly variable 

 number of aculei. A little behind the termination of 

 these lateral rows and Ijcfui-e the origin of tlie first 

 dorsal fin, we usually find in old specimens 1 — 3 true 

 lateral aculei (set at the extreme side-margin), in 

 most cases the largest on the tail, seldom of equal 

 number on both sides. These few lateral aculei at the 

 said point and those occupying the space between the 

 two fins are, though not constant, good characters, 

 where they are present, of the Thornback. The extra- 

 ordinary aculei are so variable, botii in distribution 

 and number, that no rule can be stated. They seem- 

 ingly appear a short time before the period of puberty, 

 for in all young specimens there is not even a sign of 

 their presence. The}- are most numerous in middle- 

 aged females, but in very old ones most of them have 

 again disappeared". Thej' are exti-emely seldom sym- 

 metrical, sometimes preponderating in number on the 

 dorsal side, sometimes on the ventral; sometimes scat- 

 tered, sometimes collected in groups. Their basal scutes 

 are often of considerable extent. Among the Scandi- 

 navian species of the family the Thornback is the only 

 one in which aculei appear on the ventral side. 



The coloration of the dorsal side is yellowish gray, 

 with a number of large, I'ound, whitish yellow spots of 

 varj'ing size and without s^'inmetry. Between these 

 appear smaller, black spots, like round dots, which 

 gather round the former and compose black frames, 

 sharply defined especially in young specimens. Some- 

 times there also occur in old individuals large ocelli, cir- 

 cular black spots with light margin, in one or two pairs 

 on the dorsal side. The ventral side is wliite, with a 

 dash of violet round the margins of the fins. On the 

 tail the dark colour now and then, especially in young 

 specimens, forms several (up to 6 — 8) broad transverse 

 bands, most distinct on the under surface thereof. 



The sex is manifested externally, in part and with 

 most clearness, by the large pterygopodia of the male 

 and the cards of spines peculiar to him on the upper 



surface of the pectoral fins — two patches of erectile 

 sjjines on the sides of the orbital region and another 

 pair of larger patches within the otiter angles of the 

 fins — in part by several other differences already no- 

 ticed. However distinct all these characteristics may 

 be at an advanced age, during youth they are wanting 

 or only subindicated, and at first the sexes are exter- 

 nally indistinguishable. As the time of puberty ap- 

 proaches, they all appear almost simultaneously, and 

 afterwards the difference bet^veen the sexes grows more 

 marked year by year. In a male 216 mm. long (pre- 

 sumably a year old) taken in August, ]\Ialm estimated 

 the length of the pterygopodia at only ?> mm. In a 

 male about 42 cm. long Fries found the ]jterygopodia 

 still quite small and short, their tips extending only a 

 little more than half-way along the ventral fins; there 

 were no signs of cards; the teeth were still of a gra- 

 nular, lozenged and blunt form; the ventral side of 

 the body was quite smooth, only a i'ew spots (the tip 

 of the snout and the sides of the belly) being rough 

 to the touch ; there were no extraordinary aculei, and 

 of the ordinary caudal aculei only the median row was 

 present. In a specimen 52 cm. long the circumstances 

 were essentially the same, only that the pterj'gopodia 

 were somewhat longer in relation to the \entral fins, 

 and the ventral side of the body was rougher, especially 

 under the tail. But in an individual rather more than 

 6U cm. long the pterygopodia are so developed that 

 their tips extend more than half-way along the tail, 

 and all the other characteristics of the male have ap- 

 peared, though the cards are still small, containing 

 few spines, and these set in 2 or o rows, whereas in 

 larger and older specimens as many as 6 — 8 rows 

 ma}' be counted, each containing some twenty spines 

 or more. 



The Thornback is the commonest of all the Swe- 

 dish Rays. In the Sound it occurs southwards to the 

 shallows off' Saltholm (Winther). It has occasionally 

 been met with in the south-west of the Baltic, on the 

 east coast of Schleswig-Holstein (Schonevelde and 

 MoBius and Heixcke) and the north coast of Mecklen- 

 burg (Boll''). It is most plentiful in the Cattegat 

 and the North Sea. To the nortli, according to Storm, 

 its range probably does not extend beyond the neigh- 

 bourhood of Trondhjem. To the south it penetrates into 



■■ Fries met witli very olil males .is well as females destitute of a single extraordinary aculeiis. 

 ' Die Ostsee, Arcli. Ver. Fr. Naliirg. Mcckl., Heft. I, p. 89 (sep.). 



