The Latero-Sensory Canals and Related Bones in Fishes. 439 



trie with the hind edge of the supraclavicular, strongly but loosely 

 attached to that bone by membrane. 



The supi'atemporal commissure arises from the main infraorbital 

 canal slightly posterior to the hind edge of the auto-squamosal, and 

 from there runs mesially and slightly forward approximately parallel 

 to and slightly behind the dorso-posterior edge of the skull, between 

 that edge and the first row of scales of the trunk. A small Y-shaped 

 tubular ossicle encloses the point of origin of the canal from the main 

 infraorbital canal. In this possession of a supratemporal canal enclosed 

 in independent extrascapular ossicles, Moxostoma aureolum differs 

 markedly from all the other Ostariophysi as yet referred to, and, if 

 Sagemehl's statements can be depended on, must differ even from 

 Moxostoma sucetta. For Sagemehl says, of all the Cyprinidae that 

 he examined, that the extrascapulars are reduced to little scale-like 

 bones lying at the hind edge of the squamosal, and that the supra- 

 temporal commissure lies, in all of them, in the parietals. 



The supraorbital canal begins on the antero-mesial aspect of the 

 anterior nasal aperture, and from there runs backward in a wavy line 

 almost to the dorso-latero-posterior corner of the auto-squamosal 

 (pterotic), where it ends close to but not in communication with the 

 main infraorbital canal. This course of this canal thus strongly 

 resembles that of the same canal in Macrodon, while a very slight 

 change in the position of the hind end of the canal would produce 

 the arrangement shown by Cole \25] in Chimaera. In the anterior 

 half of its course the canal lies directly superficial to the prefrontal 

 and frontal bones of Sagemehl's descriptions of Catostomus teres, but 

 widely separated from those bones by a thick, porous, dermal tissue. 

 In the posterior half of its course it lies on the external surface of 

 the dilatator operculi, and the ossicles that here enclose it, lie in the 

 membrane that covers the outer surface of that muscle. In the 

 anterior part of its course the enclosing ossicles lie in the outer edge 

 of a vertical, membranous band that rises from the outer surface of 

 an anterior prolongation of the membrane that covers the dilatator 

 muscle, the membrane here lying close upon the outer surface of the 

 frontal and prefrontal bones. 



