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Show 1897.] P R E S E N C E O E RIBS I N P O L Y U D O N. 723 In one or two works (Huxley's 'Anatomy of Vertebrated Animals,' p. 139, and the ' Text-book of Zoology' by Boas [English transl. by Kirkaldy and Pollard, p. 361]) statements occur which imply the absence of ribs in some existing Ganoids, and, as there is no question as to their presence in Acipenser, Polypterus, Anna, and Lepidosteus, the statements in question presumably refer to Polyodon. In others, again, no mention is made of the presence or absence of ribs in Polyodon, although references to the corresponding structures in Acipenser are sufficiently frequent. These quotations are sufficient to prove that the question of the presence or absence of ribs in Polyodon has been the subject of several contradictory statements, and is still involved in no little obscurity. Lateral view of a portion of the auterior section of the vertebral column of Polyodon folium. bv., inferior vertebral arch or " basi-ventral" cartilage ; bd., superior vertebral arch or " basi-dorsal " element; he, haemal canal; id., neural intercalary or interdorsal element; iv., inter-ventral or haemal iutercalary cartilage ; lg., ligament; nc, notochord ; n.s., neural spine ; r., rib. With regard to the actual facts of the case there can be no doubt as to the presence of ribs in Polyodon. In a specimen about 40 inches in length I found a series of fifteen simple, filament-like, cartilaginous ribs, commencing anteriorly near the point where the superior vertebral arches first commence distinctly to differentiate themselves from the continuous cartilaginous mass which is formed by the fusion of certain of the anterior arches with the chondro-cranium, and terminating a little posterior to the anterior half of the pre-cloacal section of the vertebral column. The third to the fifth ribs, inclusive, are perhaps the longest, being about 7 m m . in length and about 1 m m . in thickness. The first and second are a trifle shorter, but behind the fifth the ribs rapidly decrease in size until the hindermost of the series are less than 1 m m . in length, being, in fact, simple nodules of cartilage. Each rib (fig., r) is rather loosely connected by ligament (lg.) with the hinder extremity of a longi- |