J, TF. Judd — On Volcanos. 53 



The zoological position of Sesjperornis is evidently in the Odon- 

 tornithes ; but the insertion of the teeth in grooves, the absence of a 

 keel on the sternum, and the wide difference in the vertebra require 

 that it be placed in a distinct order, which may be called Odontolcce, 

 in allusion to the position of the teeth in grooves. 



The two orders of birds with teeth would then be distinguished 

 as follows : — 



Sub-class, Odontornithes (or Ayes Dentate). 



A. Teeth m sockets. Vertebras biconcave. Stermim witb keel. "Wings well 



developed. Order, Odontotoiim^. 



B. Teeth in grooves. Vertebrse as in recent birds. Sternum without keel. 



"Wings rudimentary. Order, Odontolc^. 



In comparing Ichthyornis and Hesperornis, it will be noticed that 

 the combination of characters in each is very remarkable, and quite 

 the reverse of what would naturally be expected. The former has 

 teeth in distinct sockets, with biconcave vertebrse ; while the latter 

 has teeth in grooves, and yet vertebrae similar to those of modern 

 birds. In point of size, and means of locomotion, the two present 

 the most marked contrast. The fact that two birds,, so entirely dif- 

 ferent, living together during the Cretaceous, should have been re- 

 covered in such perfect preservation, suggests what we may yet 

 hope to learn of life in that period. 



The geological horizon of all the Odontornitlies now known is the 

 Upper Cretaceous. The associated vertebrate fossils are mainly 

 Mosasauroid reptiles and Pterodactyls. 



A full description with plates of all the known Odontornitlies is 

 is now being prepared by the writer. 



Yale College, New Haven, Oct. l^th, 1875. 



EXPLANATION OF PLATE II. 



Figs. 1-4. Ichthyornis dispar, Marsh. Twice natural size. 

 Fig. 1. Left lower jaw ; top view. 



,, 2, Left lower jaw ; side view. 



„ 3. Cervical vertebra ; side view. 



,, 4. Same vertebra ; front view. 

 Figs. 5-9. Hesperornis regalis, Marsh. 



Fig. 5. Left lower jaw; side view ; half natural size. 



,, 6. Left lower jaw; top view; half natural size, 



,, 7. Dorsal vertebra ; side view; natural size. 



,, 8. Same vertebra ; front view ; natural size, 



„ 9. Tooth ; four times natural size. 



II. — Contributions to the Study of Yoloanos. 

 By John W. Judd, F.G.S. 

 Second Series. — The Ancient Yoloanos of Europe. 



IN the preceding chapters we have endeavoured to throw light ujDon 

 some of the more salient characters of volcanos — the features 

 of their architecture, the nature of their products, and the peculiari- 

 ties of their attendant phenomena. In doing so, however, we have 

 preferred to select our illustrations from some of the less familiar, 

 though, as we hope to have shown, by no means less interesting 

 volcanos of our continent ; and have of set purpose avoided the 



