354 FLATFISHES (HFTEROSOMATA) 



Statistical studies of Plaice from the Barents Sea, Baltic, Helgoland, East Scotland, 

 and the south-western North Sea, have been made by Duncker and others. ' The 

 Baltic Plaice would appear to form a distinct race, characterised by the reduced 

 numbers of dorsal and anal rays (average about 5 rays in each fin), and consequently 

 a slight increase in the length of the caudal peduncle : a small reduction in the number 

 of vertebra; (average about -75) : and in the number of rays of the pectoral fin (average 

 about '5 to -75) ; in addition, the spinulation of the males is generally much more 

 marked, and the fish mature at a smaller size. The Plaice of the Cattegat agree 

 with those of the North Sea in the numbers of vertebra; and dorsal and anal rays, 

 and with those of the Baltic in the number of pectoral rays, differing from both in 

 having a deeper body. Slight differences have been demonstrated between samples 

 from various localities in the North Sea and Channel, but these are regarded as 

 merely " Lokalformen " by Duncker. Large series of specimens from Iceland and 

 from the White Sea have not yet been investigated. 



The following table shows the numbers of dorsal, anal and pectoral rays in specimens 

 in the British Museum collection from four selected regions : 



Locahiv. Dnrsal rays. Anal rays. Pectoral rays. 



Baltic (8) . 

 North Sea (25) 

 Channel (20) 

 Iceland (8) . 



It is possible that the Baltic race will eventually come to be regarded as a distinct 

 subspecies — Pleuronectes platessa baliica, Nilsson. 



Lonnberg (1894, Overs. Vet.-Akad. Forh., li, p. 582) has described a supposed 

 hybrid Pleuronectes platessa x Glyptocephalus cynoglossus from the Cattegat. 



Hybrid Plaice and Flounder. 



PUuroni-clts fleius (part), Xilssoii, 183J, Prodr. Ithth. Scand., p. 55. 



Platessa pseudofiesus,' Gottsche, 1835, Arch. Naturgesch., i (2), p. 143 ; Mobius and Heinckc, 1883, 



Fische Ostsee, p. 92 ; Lenz, 1891, Fische Travemiinder Bucht, p. 10 ; Smitt, 1893, Scand. 



Fish., i, pp. 393, 403; Lonnberg, 1894, Overs. Vet.-Akad. Forh., li, p. 579 ; Duncker, 1896, 



Wiss. Meeresuntersuch., Abt. Kiel., .n.f., i (2), p. 76. 



Depth of body about twice in the length, length of head j3 to 3 J. Snout as long 

 as or a little longer than eye, diameter of which is 6J to 7 in length of head , inter- 

 orbital ridge naked or with some rudimentary scales ; postocular ridge consisting 

 of several small, obtuse prominences, more or less joined together to form a rugose 

 ridge, which ends in a larger prominence above the operculum and a smaller one 

 just behind it. Maxillan,' extendmg to below anterior part of eye, length on ocular 

 side 4, on blind side 3^ to 35 in that of head ; lower jaw about 3 in head. Teeth 

 somewhat compressed, truncate, close-set, but not forming a continuous cutting 



edge ; dental formula J^ — ~ — 2_. g gill-rakers on lower part of antenor arch : 



7-10 -I- 19-21 

 lower pharyngeals rather broad and massive, width about 3 m length, each with 

 3 rows of obtuse teeth, one along each side of the pharyngeal bone, with some odd. 



' See Malm, 1882, Goteb. Xat. Mus. Zool. Afdel., Arsskr., in, (1881), p. 23 ; Holt, 1S94, J. Mar 

 Biol. Ass., (2)iii,p. 194 ; Duncker, 1895, Zool. Anz., xviii.p. 53 ; Duncker, 1896, Wiss. Meeresunter- 

 such., Abt. Kiel, N.r., i (2), p. 47 ; Cunningham, 1897, J. Mar. Biol. Ass., (2) iv, p. 315 ; Kyle, 1901, 

 Rep. Fish. Board Scotland, xviii (iii) (1900), p. 189; Duncker, 1913, Jahrb. Hamburg Wiss. Anst., 

 XXX (2), (1912), p. 197 : Keilhack, 1913, Wiss. Meeresuntersuch., Abt. Helgoland, -n.f., x, p. 168 ; 

 Redeke, 1915, Rapp. proc.-verb. explor. mer., xxii, p. 4 ; Ssytsch-Awerinzewa, 1929, Zool. Anz., 

 Ixxx, p. 149 ; Racbmanowa, 1929, Zool. Anz., Ixxxv, p. 139. 



^ Some of the descriptions of P. pseiidoflesus may refer to the spinulatcd males of the Baltic race 

 of P. platessa. 



