1904.] OSTEOLOGY OF CLUPEOID FISHES. 459 



Opercular Series (text-figs. 123 and 124, pp. 456, 457).— The 

 opercular and subopercular bones are of average proportions ; the 

 latter is relatively larger in Cliqjea harengnjS than in Clapeafinta. 

 There are seven branch iostegal rays in Clupea finta — five rather 

 slender ones borne by the ceratohyal, and two broader ones 

 attached to the outer face of the epihyal. In Clupea harengiis 

 the numbers are five and three respectively. 



Hyohranchial Series (text-fig. 125, p. 458). — The lower hypohyal 

 of Clupea harengus is larger than the upper. The urohyal is large 

 and extends back behind the posteiior extremity of the third 

 basibranchial. The glossohyal is a conical cartilage, flanked on 

 its upper surface by a thin membrane-bone. This is covered by 

 mucous membrane bearing small teeth ; but the teeth, although 

 they may leave scars when removed, are not intimately attached 

 to the bone. The only elements of the hyobranchial skeleton 

 which bear teeth anchylosed with the bone are the fifth cerato- 

 branchials. 



The second basibranchial bears fixed on its upper surface a 

 toothless membrane-bone which extends forward and backward 

 over, but is readily i-emovable from, the first and third basi- 

 branchials. The equivalent membrane-bone in Chq^ea finta does 

 not extend over the third basibranchial. The fourth and fifth 

 basibranchials are represented by an elongated cartilage which is 

 continued back in the form of a slender rod some distance behind 

 the point at which the fifth ceratobranchials are attached. 



The fourth epibranchial is rather large and flat, and serves 

 to supjDort the wall of the epibranchial organ. Its posterior 

 extremity is united with the upper end of the fifth cerato- 

 branchial by a ligament which is the exact equivalent of that 

 slender bar of cartilage which in Engraulis represents the fifth 

 epibranchial {cf. text- figs. 125 B and 135 B, pp. 458 and 475). 

 In Ghipea alosa Gegenbaur (Morph. Jahrb. iv. Suppl. p. 24 and 

 pi. ii. fig. 13, Chqiea indgaris or Alosa vulgaris) has figured a 

 fifth epibranchial cartilage. The first pharyngobranchial is small 

 and cai-tilaginous, but a well-developed spicidar bone rises 

 vertically from the upper surface of the anterior extremity of 

 the first epibranchial. 



Pelloxa motius. 



In Pellona motius (Brit. Mus. 1888.11.6.64, E. C. Madras) the 

 top of the cranium is much narrower than in Clupea^ and the two 

 principal longitudinal ridges on the upper surface are closer 

 together and more nearly pai-aUel. The part of the cranium 

 behind the orbit is greatly reduced in an antero-posterior direc- 

 tion, but not in a vertical direction. The temporal foramen is 

 smaller than in Clupea and the pre-epiotic fossa shallower. 



The pro-otic, squamosal, and exoccipital appear to be completely 

 hollowed out for the accommodation of the csecal diverticiila of 

 the swim-bladder ; but the exact relations of the bullae can only 

 be made out by freely incising the hinder part of the cranium, 



