80 



OLD RED SANDSTONE FISHES. 



by being more antero-posteriorly oblong in shape, and having the articular notch 

 on its inner side rather more forward in position. This inner margin is affixed 

 to the outer aspect of the lateral and angular plates, while the outer edge rests on 

 the prolongation of the anterior ventro-lateral plate of the body in front of the 

 brachial articulation, the cleft between them having probably functioned as a gill- 

 opening. 



The maxillary plates of Asterolepis maxima are still unknown. 



The course of the sensory grooves on the head has been indicated in the defini- 

 tion of the genus, and is so clearly exhibited in fig. 1, PI. XVII, as to require no 

 further description. 



Body-Carapace. — The anterior median dorsal plate (PI. XVI, fig. 1) is somewhat 

 lanceolate or pointed-elliptical in contour, the sides being convex and the anterior 

 margin very short, — indeed, less than half the width of the posterior. The upper 

 surface is gently convex in front, but decidedly carinated behind the middle : and at 

 the posterior extremity there is a depressed triangular articular area, whose base is 

 formed by the whole of the hinder margin of the plate, and which is covered by the 

 pointed anterior extremity of the posterior median dorsal. No other articular 

 surface is seen on the dorsal aspect, but on looking at the plate from below 

 (woodcut, Fig. 40) the anterior margin is seen to be excavated for overlapping the 

 median occipital of the head, while along the right and left margins two narrow 



Fig. 40. Fig. 41. 



Pig. 40. — Internal aspect of the anterior median dorsal plate, a., surface in front overlapping the median 

 occipital ; b. and c, surfaces overlapping the anterior and posterior dorso-lateral plates respectively. 



Fig. 41. — Internal aspect of the posterior median dorsal plate restored, d. and e., surfaces overlapping 

 the right and left dorso-lateral plates respectively ; /., surface overlapping the anterior median dorsal. 



bands, anterior and posterior, are excavated to overlap the corresponding margins 

 of the anterior and posterior dorso-lateral plates. 



The posterior median dorsal plate (PI. XVI, fig. 2 ; woodcut, Fig. 41) somewhat 



