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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 attachments 

 that are more or less fenestrated. There are also numerous 

 strands on the inner side of the flaps. Stohr (76) and Boas 

 ('80) have published accounts of conus forms in a number of 

 the 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 found 

 in the hearts of Amia on the side of the ganoids and of Butyrinus 

 among the teleosts. The former has three valves of four cusps 

 each. Of these cusps two are reduced in size in each valve. 

 Butyrinus has two valves, the anterior with two cusps, the pos- 

 terior with four as in Amia. Senior ('07) has recently described 

 the conus of Tarpon which contains two valves of but two cusps 

 each. With these exceptions almost all teleosts have a single 



