2 AGNATHA. 



apparently formed of structureless concentric lamellae, without 

 any trace of vascular canals or capillaries ; and the substance of 

 the fossils is chiefly carbonate of lime. Some conodonts consist 

 only of a single cusp, others of a series of cusps upon one base ; 

 and minute plates, ornamented on one side with tubercles, are 

 sometimes found in association with them. They may even be 



FIG. 1. 



Palceospondylus gunni ; ventral aspect of head, lateral aspect of vertebral 

 column, restored by E. H. Traquair, nearly twice nat. size. L. Old Eed 

 Sandstone ; Caithness, a, separate small lobe ; b, anterior depression or 

 fenestra ; c, posterior depression or fenestra ; d.c., dorsal cirri; I.e., long 

 lateral cirri ; n., supposed narial opening; p.a, parachordal portion of skull; 

 t.p., trabeculo-palatine portion of skull ; v.c., ventral cirri ; x, problematical 

 post- occipital plates. 



the teeth of unknown Nudibranchs or Annelids, or the hooks of 

 Gephalopods, and can thus be dismissed as fragments too 

 inconclusive for consideration here. 



