PISCES 



169 



present Skates and Rays than anything else and probably having 

 similar but more sluggish habits. Thelodus and Lanarkia, the restored 



FIG. 99. A group of ostracoderms and their kin. A and G directly after 

 Patten; the rest from Patten, after Traquair. A, Bothriolepis canadensis; B, 

 Thelodus; C, Lanarkia; D, Birkenia; E, Lasanius; F, Drepanaspis; G, Cephal- 

 aspis. (Redrawn after Patten.) 



outlines of which are shown in Fig. 99 B and C, seem to have had an 

 exoskeleton composed of " a uniform covering of hollow pointed spines, 

 devoid of basal plate, and open below." These spines are composed 



