. Journal of morphology. Fig. 1 A conus arteriosus cut along the midventral line and spread open,this specimen there are but three valves, one of which has an extra cusp. In JOUKNAL OF MOEPHOLOOT, VOL. 23, NO. 3 414 A. H. DANFORTH of teleosts, is usually the one best developed. The cusps them-selves are of the characteristic type described by Stohr (76),having a thick middle portion and thin lateral attachmentsthat are more or less fenestrated. There are also numerousstrands on the inner side of the flaps. Stohr (76) and Boas(80) have published accounts of conus forms in a number ofthe ganoids
. Journal of morphology. Fig. 1 A conus arteriosus cut along the midventral line and spread open,this specimen there are but three valves, one of which has an extra cusp. In JOUKNAL OF MOEPHOLOOT, VOL. 23, NO. 3 414 A. H. DANFORTH of teleosts, is usually the one best developed. The cusps them-selves are of the characteristic type described by Stohr (76),having a thick middle portion and thin lateral attachmentsthat are more or less fenestrated. There are also numerousstrands on the inner side of the flaps. Stohr (76) and Boas(80) have published accounts of conus forms in a number ofthe ganoids, but neither of them includes Polyodon in his de-scriptions. These authors point out that a beautiful transi-. Fig. 2 A conus with four well developed valves tion from the ganoid to the teleostean type of conus is foundin the hearts of Amia on the side of the ganoids and of Butyrinusamong the teleosts. The former has three valves of four cuspseach. Of these cusps two are reduced in size in each has two valves, the anterior with two cusps, the pos-terior with four as in Amia. Senior (07) has recently describedthe conus of Tarpon which contains two valves of but two cuspseach. With these exceptions almost all teleosts have a single THE HEART AND ARTERIES OF POLYODON 415 valve of two cusps. If it were desirable to show a still closerseries of gradations, the variable conus of Polyodon might beplaced before that of Amia in a series leading back through suchforms as Lepidosteus and Polypterus to the complicated struc-ture found among the Dipnoi. Such a finely graded series,however suggestive it might be, would probably not correspondto any line of descent. The morphological value of
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