CLASSIFICATION OF VERTED RATA 



Super-CLASS HYPOSTOMATA 



Under the name of Hypostomata I separate the 

 OSTRACODERMI, Cope, as a group equivalent to and inter- 

 mediate between Cyclo- and Gnathostomata. 



Craniota without " limbs " and without jaws. Vertebral 

 column acentrous. With strongly developed dermal skeleton. 



I. CLASS HETEROSTRACI, Lankester 



Without paired appendages. Trunk and tail with rhomboid 

 scales and fish-like. Skeleton with calcifications, but without 

 bone and without enamel. 



Pteraspis. Lower Old Red Sandstone, England. 



II. CLASS OSTEOSTRACI, Lankester 



Without paired appendages. Calcifications, with bone 

 corpuscles, with or without enamel. 



Cephalaspis. Lower Old Red Sandstone, Europe and 

 Canada. Even already in the Ludlow strata, upper- 

 most Silurian. 

 Auchenaspis. Upper Silurian of Oesel, Eastern Baltic. 



III. CLASS ANTIARCHA, Smith Woodward 



With bone corpuscles, and with " ganoine. One pair of 

 paddle-like appendages, covered with plates. 

 Asterolepis. Devonian, Russia. 



Pterichthy s. Lower Old Red of Scotland, Germany, 

 Russia. Possibly also in the upper Silurian strata 

 of the Eastern Baltic. 



