948 DR. W. G. HIDEWOOD ON THE [XoV. 28, 



between the first and second eiferent branchial vessels is wanting, 

 owing to the backward extension of the circuhis to the point of 

 entry of the second branchial vessels into the aorta. The same 

 feature is to be observed in Balistes (fig. o), where the aortic 

 stem between the second vessel and the common trunk of the 

 third and fourth is also suppressed. The cceliaco-meseuteric artery 

 of Balistes arises, not from the aorta, but from the third and 

 fourth branchial vessels of the right side, iu)mediately after their 

 anastomosis. 



If vce disref];ard the modification of the efferent branchial circu- 

 lation brought about in Gymnan-hus hj the increased functional 

 importance of the swim -bladder, the efferent branchial system of 

 this genus can be seen, from the description and figure published 

 by Hyrtl (11. p. 11, and pi. 4. hg. 4), to conform with the type 

 which characterizes subgroup A c. 



Further Eemarks on G-roup B. 



The efferent branchial system of Scomber (fig. 6) bears a close 

 resemblance to that of Salmo (fig. 7), but the cceliaco-mesenterie 

 artery arises from the aorta immediately behind the fourth effr'reut 

 branchial vessels and the subclavian arteries some distance farther 

 back, whereas in Salmo the positions of the cceliaco-mesenterie and 

 subcla\ian arteries are reversed. In the figure of Scomber given 

 by Stannius (23. pi. v. fig. 4) the circulus cephalicus appears 

 much too large, and the interval between the circulus and the 

 entry of the third and fourth branchial vessels into the aorta too 

 short. 



In Salmo irutta, as also in Osmerus and Corer/onus, the dorsal 

 aorta is wide and thin-w ailed ; but this is not the case in Sahno 

 salar. The distance between the posterior angle of the circulus 

 and the point of entry of the third eft'erent branchial vessel is 

 proportionately longer in Coregoims than in Salmo scilar. and pro- 

 portionately shorter in Salmo tniita. A very reliable figure of the 

 efferent branchial system of S. tmtfa has been given bv Yogt 

 (1. pi. L. fig. 2). The figure by Stannius of S. salar (23. pi. v. 

 fig. 3) is incomplete, but is correct so far as it goes. In Hypo- 

 fhthalmiclithys both the cceliaco-mesenterie and the subclavian 

 arteries arise some distance behind the fourth efferent vessel. The 

 circulus in this genus is broader than long. 



In Hippoqlosxus (fig. 9), Pleuronectes, Miigil (fig. 8), Esox 

 (fig. 15), and Marcvsenms the distance between the posterior 

 angle of the circulus cephalicus and the point of entry of the 

 common trunk of the third and fourth branchial vessels is so short 

 that these forms approach somewhat closely those included in 

 subgroups Ch and Cc. In Pleuronectes the circulus cephalicus is 

 longer than broid, whereas in Hi ppoj/lossus it is broader than long; 

 the anterior carotids are closer together, and the transverse com- 

 missure between them is shorter than in Jlippoglossvs. The 

 common trunk formed by the union of the third and fourth 

 branchial vessels of the right side is much shorter than that 



