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Show 948 DR. W. G. RIDEWOOD ON THE [Nov. 28, between the first and second efferent branchial vessels is wanting, owing to the backward extension of the circulus to the point of entry of the second branchial vessels into the aorta. The same feature is to be observed in Balistes (fig. 5), where the aortic stem between the second vessel and the common trunk of tbe third and fourth is also suppressed. The coeliaco-mesenteric artery of Balistes arises, not from the aorta, but from the third and fourth branchial vessels of the right side, immediately after their anastomosis. If we disregard the modification of the efferent branchial circulation brought about in Gymnarchus by 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 pl. 4. fig. 4), to conform with the type which characterizes subgroup A c. FURTHER REMARKS ON GROUP B. The efferent branchial system of Scomber (fig. 6) bears a close resemblance to that of Salmo (fig. 7), but the coeliaco-mesenteric artery arises from the aorta immediately behind the fourth efferent branchial vessels and the subclavian arteries some distance farther back, whereas in Salmo the positions of the coeliaco-mesenteric and subclavian arteries are reversed. In the figure of Scomber given by Stannius (23. pl. 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 Coregonus, the dorsal aorta is wide and thin-walled • but this is not the case in Salmo salar. The distance between the posterior angle of the circulus and the point of entry of the third efferent branchial vessel is proportionately longer in Coregonus than in Salmo salar, and proportionately shorter in Salmo trutta. A very reliable figure of the efferent branchial system of S. trutta has been given by Yogt (1. pl. L. fig. 2). The figure by Stannius of S. salar (23. pl. v. fig. 3) is incomplete, but is correct so far as it goes. In Hypo-phthalmichthys both the coeliaco-mesenteric and the subclavian arteries arise some distance behind the fourth efferent vessel. The circulus in this genus is broader than long. In Hippoglosstis (fig. 9), Pleuronectes, Mugil (fig. 8), Esox (fig. 15), and Marcusenius 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 Cb and Cc. In Pleuronectes the circulus cephalicus is longer than broad, whereas in Hippoglossus it is broader than long • the anterior carotids are closer together, and the transverse commissure between them is shorter than in ILippoglossus. The common trunk formed by the union of the third and fourth branchial vessels of the right side is much shorter than that |