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Show 950 DR. W. G. RIDEWOOD ON THE [NOV. 28, The efferent branchial vessels of Chanos have been described and figured by Hyrtl (12. pl. i. fig. 1). The first and second vessels open into the circulus cephalicus, the third some distance farther back into the median aorta, while the vessels from the fourth gills, after uniting with those from the epibranchial organs, unite with one another and open into the aorta at a point as far behind the opening of the third branchial vessel as the latter is behind the circulus cephalicus. The genus thus falls into group B, but, owing to the exceptional disposition of the fourth pair of vessels, it cannot be included in any of the three subgroups recognized. FURTHER REMARKS ON GROUP C. The circulus cephalicus is narrow in front in Labrax (fig. 17), but it is broad in the Siluroids Liocassis (fig. 18), Callichthys (fig. 19), and Clarias (fig. 20). In Labrax the coeliaco-mesenteric artery arises from the aorta immediately behind the fourth efferent branchial. It has the same relations in Clarias, but is somewhat more posterior in Callichthys, and considerably so in Liocassis. The subclavian arteries arise behind the coeliaco-mesenteric artery in Labrax, Clarias, and Callichthys, but close behind the fourth branchial vessel in Liocassis. Although Clarias is introduced into the subgroup C a, it really occupies an intermediate position between C a and C b, since there is a very short common trunk on each side between the last two branchial vessels and the aorta. The genus Heterotis I have not been able to examine, but it is tolerably certain, from the description given by Hyrtl (9. p. 87), that it should be included in the subgroup Ca. In Mullus and Corvina the disposition of the coeliaco-mesenteric and subclavian arteries is as in Perca (fig. 21), but the circulus cephalicus is broader in front. The circulus has the form of a regular heptagon in Mullus, while in Corvina it is pear-shaped, the broad end being anterior. In Equula it is oval in shape and longer than broad ; but otherwise the relations of the parts are as in Perca. With regard to Perca itself, Hatchett Jackson, in his edition of Rolleston's 'Forms of Animal Life'(21. p. 88), states that the " coeliaco-mesehteric artery * * * springs from the right epibranchial artery before it fuses with its fellow." This does not accord with my own observations. Hyrtl in his figure of Lucio-perca (7. pl. i. fig. 1) shows the common trunks of the third and fourth branchial vessels entering the aorta at some distance from the posterior angle of the circulus. The transverse commissure, also, between the anterior carotids (" die vorderen oder kleinen Kopfarterien ") is situated farther forward than in Perca. In Zeus (fig. 22) the circulus is broader, and the coeliaco-mesenteric artery arises, not from the aorta, but from the common trunk of the last two branchial vessels of the right side. Zoarces resembles Anarrhichas (fig. 23) in tbe oval shape of the circulus and in the narrow anterior prolongation of the latter, but the |