986 



SCAXDINAVIAX FISHES. 



witli the posterior margin of the eyes, the length of 

 the cheek behind them being less than its height below 

 the eyes. Tlu' length of the lower jaw is 14 — 13 % 

 of that of tlie body" or al)out 62 — o8 % of that of the 

 head. The height of the dental piirt is less than in 

 the Herring, measui'ing about ' ., of the length of the 

 lower jaw. At the symphysis the lower jaw is most 

 like that of the Pilchard and oidy slightly prominent; 

 Imt in old or lean specimens the symphysis is more 

 truncate (deeper), and has two pairs of compai'atively 

 small chin-protuberances above. The jaw-teeth dis- 

 appear more or less comi)letely with age, most in the 

 AUice Sliad: Imt even in old specimens a fairly regular 

 row \w,\\ lie found on tlie intermaxillaries, a tooth or 

 two in tlie front of tlie lower jaw, and traces of the 

 dentiform crenelation on tlie hind part of tlie maxil- 

 laries. Tliere ai'e no other teeth in tlie mouth. The 

 differences in the gill-rakers of the two varieties have 

 been mentioned above, and may l)e seen in the tigures. 

 Tlie oijcrcuhu' apparatus differs from that of the Her- 

 ring in the greater extension of the jireoperculum back- 

 wards and downwards and in a con'es]KMiding reduc- 

 tion of the ojierculum below, the obli(|uely set inferior 

 margin (the suture with the subojierculum), which is 

 fairly straight or incurved, measuring oidy about 17 V3 

 —21 % of the length of tiie liead, S.")— 47 %'' of that 

 of the maxillaries, or 29 — 3.5 % of that of the lower 

 jaw. An equally perceptible alteration of growth a|)- 

 pears in the form of the suboperculnm, which becomes 

 narrower, as n, rule, during gro\vtli, its breadth at. tiie 

 middle decreasing from about 60 to 40 % of the length 

 of the said suture. As the length of the body increas- 

 es from 12 to 40 cm., tlie postorbital length of the 

 head rises from about 4-5 '/a ^^o 58 % of the entire 

 length thereof, or fi-om about 25'/. to 30 % of tlie 

 distance between the dorsal fin and the articular knobs 

 of the maxillai'ies. When the postorbital length is 

 measured in an oblique direction (to the lower posterior 



angle of the opercidum), these percentages increase re- 

 spectively' from about 52'-., to 62' ^ '"icl from 29'/o to 32. 



The length of the pectoral fins, which are oblique- 

 ly pointed, is about 16 — 14 %, that of the ventral 

 fins about 10' ., — 8' . %, of the length of the body. 

 The i)i-eabdominal length varies between about 22 and 

 26 ?o, the postabdominal between 21 and 24'/^ %, of 

 the length of the body. 



The dorsal fin begins at a distance fnnii the ar- 

 ticular knobs of the maxillaries measuring about 42 — 

 44'/2 % of the length of the body, or 90—99 % of the 

 distance between the ventral tins and the same points. 

 Its height decreases with age from ;ibont 15 to 11*', 

 and the length of its base varies between about 13 

 and 15 %, of the length of the body, the latter propor- 

 tion seeming as a rule to be somewhat less in young 

 specimens than the former, greater in old. The caudal 

 fin is deeply forked, the middle rays measui'ing only 

 '/^ — '/- of the length of the longest ones, which varies 

 between about 22 '/^ and 19 % of that of the body. 

 The inferior lobe of tlic caudal tin is, ns usual, some- 

 what longer than tlie superior. 



The anal iin is of special interest from a syste- 

 matic point of view. The form is indeed highlj' vari- 

 able, but we have failed to discover any rule for its 

 variations. Sometimes the Iin is comparatively high, 

 the length of its longest ray measuring as much as 

 "/s of its liase. In other specimens it is as low as in 

 the pi-eceding Clupeoids, the height lieing but little 

 more than '/^ of the base. But the extent of the tin, 

 the length of its base, seems to afford a distinction 

 both between tlie sexes and the varieties. In each 

 variety of the Shad, so far as onr observations have 

 been carried, the females have ;i comparatively longer 

 anal tin than the males; and the base of the anal fin 

 is comparatively longer in the Allice Shad than in the 

 Twaite Shad. \Ye mav liei'e adduce the following ex- 

 amples of the rule: 



11 sinks in llie oldest Shads to 12 



Alioiil 55 — 58 \ in ihe Pilcluird. 



Or even to 9 "i, jndo'ino^ by a stuffed specimen 



lereof, judging l>y a stnfEed specimen. 



