504 On the Structure and Classification of the Asterolepidae. 



EXPLANATION OF THE PLATES. 



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



m. occ. Median occipital. p. m. d. Postei-ior median dorsal. 



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



ag. Angular. p. d. I. Posterior dorso-latei'al. 



pt. m. Postmedian, a. v. I. Anterior veutro-lateral. 



p. m. Premedian. ^?. v, I. Posterior ventro-lateral. 



I. Lateral. w. v. Median ventral. 



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



mn. Mental plates, the " Uuter- 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 XVII. 



Fig. 1. Eestored 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 there- 

 fore 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 XVIII. 



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

 Asterolepis maximus, Ag. sp., much reduced. The shaded 

 area z is that overlapped by the front of the posterior median 

 dorsal plate. 



Fiy. 2. Outline of the internal surface of the same plate ; x and y, mar- 

 ginal areas overlapping the anterior and posterior dorso-lateral 

 plates respectively. 



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

 thriolepis gigmiteus, Traq. ; x, area overlapping the anterior 

 dorso-lateral. 



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

 Ag. sp., from specimens in the Edinburgh Museum. TLe over- 

 lapped 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 B. hydrophilus ; s. I., 

 the single plate representing the semilunars. 



Fig. 6. Outlines of the bones of the head of B. 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 Micrdbrachius Dickii, Peach, 

 sp., showing its articulation with the anterior dorso-laterals. 



Fig. 8. Dorsal plates of the carapace of Micrubrachins Dickii seen from 

 the internal aspect ; the outlines of the head and of one of the 

 arms are likewise shown, 



