

ANTIARCHI. 



15 



sharply bent sensory canal; but there is a conspicuous smooth band 

 immediately adjoining the posterior border, and this is further remark- 

 able for exhibiting an irregular series of minute sharp denticles different 

 in aspect from the bosses and points of the ordinary surface-ornament. 

 It appears, indeed, as if this pair of plates formed the anterior margin 

 of the mouth, covered with an overlapping lip of soft tissue and pro- 

 vided with a minute denticulation. It may be added that a very thin 

 lamina of smooth bone of uncertain size and form occurs on the visceral 

 aspect of this pair of jaw-plates, and its straight hinder margin is indi- 

 cated in the accompanying fig. 14. The typical species of Bothriolepis is 

 B. ornata, known only by fragments from the Upper Devonian of N.W. 

 Russia. Fragments of other large species occur in Scotland, while two 

 comparatively dwarfed forms are met with at Dura Den, Fifeshire 

 (B. hydrophila, fig. 15), "and at Farlow, Shropshire (B. macrocephala}. The 

 finest known specimens, about 0'2 m. in length, are those of B. canadensis 

 (figs. 13, 14), to which special reference has been made. 



Bothriolepis hydrophila ; restoration by R. H. Traquair, dorsal aspect, nat. 

 size. U. Old Red Sandstone; Dura Den, Fifeshire. a, anconeal plate; 

 ii./n.d., anterior median dorsal ; a.d.l., anterior dorso-lateral ; ar., articular; 

 m, marginal; p.d.l., posterior dorso-lateral; p.m.d., posterior median 

 dorsal ; p.v.l., posterior ventro-lateral ; doable dotted line indicating grooves 

 for sensory canal. 



Aster olepis is a genus closely resembling Pterichthys and 

 Bothriolepis, known only by fragments from the Upper Old Red 

 Sandstone of Scotland and Livonia. 



