PLATE XIV 



Fir. 



1. Horizontal section about the middle layer of the shield of Zenmprs, magnified 50 

 diameters. 



.2. The same, magnified .200 diameters. 



3. Horizontal section of the lower layer of the same, magnified .200 diameters. 



4. Horizontal section of tubercles of Zenaspis, magnified 30 diameters. 



5. The same, magnified 120 diameters. 



0. Horizontal section of a portion of the scale of Kallosfrakon podinri, magnified 200 

 diameters. 



7. A portion of the shield of Zenaspis Salivei/i, magnified 4 diameters. The substance 

 of the shield is worn away from the right down to the left side of the 

 specimen, and thus the successive layers are exposed ; on the right hand top 

 corner the shining tubercnlar snrface ; below this the radiating stellate forms 

 due to the disposition of the vascular canals ; below this again simple hexagonal 

 or multiangular pieces completely emarginated by canals ; and lastly, horizontal 

 branching canals, causing the "fibrous structure" spoken of by Agassiz. 

 \'ertical canals are seen in section as minute dots in all the different 

 thicknesses. 



S. Vertical section of a part of the shield of Cephalaspis Lyellii, copied from Prof. 

 Huxley's paper in 'Quart. Journ. Geol. Soc.,' vol. xiv, ISoS. 



