14 AGNATHA. 



Bothriolepis (figs. 13 15). An Upper Devonian genus differing from 

 Pterichthys in its larger appendages and in minor points relating to the 

 proportions of the plates and the arrangement of the sensory canals. The 

 tail also appears to have been scaleless, no undoubted traces of this part 

 of the body having hitherto been discovered. The great interest of the 

 genus, however, consists in the arrangement of its mouth-parts, dis- 

 covered in the fine examples of B. canadensis from Scaumenac Bay, 

 Canada. Beneath the head-shield at its front extremity, (fig. 14) there 



FIG. 13. 



Bothriolepis canadensis ; diagram of head-shield, upper aspect, about one-half 

 nat. size. U. Devonian; Scaumenac Bay, Canada, ag., angular; e.L, 

 extra-lateral (operculum) ; I, lateral; l.occ., lateral occipital; m.occ., 

 median occipital; p, postmedian ; p.m., premedian ; double dotted lines 

 indicating grooves for sensory canal. (After Traquair.) 



FIG. 14. 



Bothriolepis canadensis; inferior aspect of head, showing supposed upper jaw- 

 plates, nat. size. U. Devonian ; Scaumenac Bay, Canada, n, lateral 

 notch, possibly for narial opening ; x, smooth delicate lamina of bone ; 

 bent double line indicating groove for sensory canal. (From specimens 

 in British Museum, nos. P. 676162.) 



is observed a pair of transversely elongated plates much resembling those 

 of Pterichthys, but not so extensively in contact at the median symphysis. 

 These are in contact with the edge of the dorsal shield in front, but their 

 posterior border is free and convexly arched. A notch at each outer 

 margin, as before, may indicate the opening of a nasal sac. The greater 

 part of the outer face of each plate is feebly rugose and marked by a 



