978 



SCAXDIXAVIAN FISHES. 



Subgenus; ALOSA. 



Sides of the bodij marked, at least in front, with dark spots. Lotver anterior surface of the operculum coursed 

 by more or less distinct grooves and ridges. Dorsal fin set so far forward that the distance between it and the 

 tip of the snout is less than four times the postorlntal length of the head. Inner part of the caudal lobes fur- 

 nished with foliate scales, larger than the others. 



Now that all attempts to employ the dentition as 

 a means of detining subgenera within the genus Clupea 

 liave proved futile, no better prospect of attaining this 

 object is offered, it appears, than by the different de- 

 veloijraent and position of tlie tins. But tlie subgenus 

 Alosa, which is further distinguished liy the extremely 

 feeble dentition of the mouth, is so well defined within 

 the Scandinavian fauna that no ditficulties meet us here 

 in its characterization. In exotic forms, however, as 





2i5. Scales from the Ifft side of a Pilclianl 20 cm. long (a) 

 and from a Shad 30 em. in length (/-). X 3. 



for instance in the Japanese Clupea zunasi, the striation 

 of the opercula is hardly perceptible, and the lateral 

 markings of the body are confined to a single small 

 spot on the adipose membrane of the upper scajjuiar 

 region; and in the Mediterranean Clupea aurita, where 

 the dark markings are also restricted to tlie ujiper jjart 

 of the tract round the gill-openings, the said striation 

 consists merely of a ridge crossing the anterior part of 

 the operculum in an obliquely downward direction. But 

 the other characters given in the above diagnosis range 

 these forms beside our Shads, whicli may be I'egarded 

 as the type of the subgenus, and which are usually to 

 be recognised at the first glance by tlie striation of the 

 opercula and the spots on the sides of the body, though 



the latter vary I)oth in size and distinctness, being in 

 some individuals wanting. 



The scales of this subgenus are more strongly 

 developed at the basal angles of the fins and their bases 

 than is the case in the preceding members of the genus. 

 Tlie caudal fin is covered to a great extent with scales, 

 and bears on each side two patches of these, one on 

 the upper and one on the lower lobe, among which the 

 hindmost is the largest, and is also venous. Sometimes, 

 however, these patches of scales are so thin and trans- 

 parent that they easily escape observation. At the base 

 of the dorsal fin, the upper angle of the pectoral fin, 

 and tlie outer angle of the ventral fin, we find pointed 

 scales, whicli partially conceal these fins; and rounded 

 scales overlap the lower margin of the pectoral fins, 

 covering the lo'west raj's, while the base of the anal 

 fins is also scale-clad. In texture too the scales of 

 this sul)geiuis differ from those of the preceding one, 

 the radiating grooves, \vhich are there extremely faint 

 streaks (see abo\e, p. 9.57), being here far more sharply 

 defined (fig. 245). 



Both the anal and the dorsal fins show a more 

 pointed prolongation of the outer posterior corner tiian 

 in the preceding subgenus. 



The mo.st constant character, however, is the for- 

 ward position of the dorsal fin, a character which is 

 expressed in the above diagnosis of the subgenus by a 

 comparison witii the postorbital length of the head. 

 This last measurement is relatively greater in the Shads 

 than in the true Herrings, the validity of the character 

 being thus unimpaired even wiien the trunk is siior- 

 tened, as in tiie American Menhaden, which would else 

 be referred liy the position of the dorsal fin to the 

 preceding suligenus. 



