46 Proceedings of the Royal Physical Society, 



Explanation of tup: Plates. 



(In all the figures the same letters refer to the same tilings.) 



m. occ. Median occipital. p. m. d. Posterior median dorsal. 



I. occ. Lateral occipital. a. d. I. Anterior dorso-lateral. 



ag. Angular. ^?. d. I. Posterior dorso-lateral. 



pt. m. Postmedian. a. v. I. Anterior ventro-lateral. 



p. m. Premedian. p. v. I. Posterior ventro-lateral. 



/. Lateral. m. v. Median ventral. 



e. I. Extra-lateral. ar. Articular of limb. 

 mn. Mental plates, the " Unter- a. Anconeal of limb. 



kiefer " of Pander. c. Central of limb, 



.s. I. Semilunar. m. Marginal of limb. 

 a. m. d. Anterior median dorsal. 



Plate I. 



Fig. 1. Restored outline of Pterichthys cornutus, Ag., seen from the dorsal 

 surface. The thin black lines in this and Figs. 2 and 3 denote the edges of 

 the plates which are overlapped, and therefore concealed ; the double dotted 

 lines indicate the grooves occupied by the lateral canal-system. 



Fig. 2, Restored outline of the same species seen from the ventral aspect. 



Fig. 3. Restored outline of the same species, lateral aspect. 



Fig. 4. Outline of extra-lateral plate of Pterichthys, natural size, 



Plate II. 



Fig. 1. Outline of external surface of anterior median dorsal plate of 

 Astcrolepis maximus, Ag., sp., much reduced. The shaded area z is that 

 overlapped by the front of the posterior median dorsal plate. 



Fig. 2. Outline of the internal surface of the same plate ; x and y, marginal 

 areas overlapping the anterior and posterior dorso-lateral plates respectively. 



Fig. 3. Outline of internal surface of anterior median dorsal plate of 

 Bothriolepis giganteus, Traq. ; x, area overlapping the anterior dorso-lateral. 



Fig. 4. Restored outline of the dorsal aspect of Bothriolepis hydrophilus, 

 Ag., sp., from specimens in the Edinburgh Museum. The overlapped edges 

 of the plates are not given here, but the lateral-line grooves are shown by 

 double dotted lines. 



Fig. 5. Front of anterior ventro-lateral plates of ^. hydrophilus; s. I., the 

 single plate representing the semilunars. 



Fig. 6. Outlines of the bones of the head of £. canadensis, Whiteaves, 

 from specimens in the Edinburgh Museum, except the plates filling the median 

 opening, which are copied from Whiteaves. 



Fig. 7. Anterior median dorsal plate of Microhrachiiis Dichii, Peach, sp., 

 showing its articulation with the anterior dorso-laterals. 



Fig. 8. Dorsal plates of the carapace of Microhrachius Dichii seen from the 

 internal aspect ; the outlines of the head and of one of the arms are likewise 

 shown. 



