ASTEROLEPIS MAXIMA. 77 



represented in PL XV. In this figure, which is one-fifth smaller than the 

 original, we see the internal surface of the whole dorsal part of the carapace along 

 with the cranial shield, the latter being slightly injured on the left side. The 

 general form of the animal as well as the arrangement of its plates is also exhibited 

 in the accompanying restored sketches, in which nothing is hypothetical unless 

 indicated by dotted lines. 



The carapace is flat below ; its narrow sides are nearly vertical ; the back 

 slopes gently downwards and outwards on each side, the middle line behind 

 the centre of the anterior median dorsal plate, being distinctly carinated. Seen 

 from the side, the back is gently arched antero-posteriorly, but at the nape the 

 profile of the head sinks down at an angle of 45° to the horizontal plane. The 

 general shape of the head and body thus agrees pretty well with that in Pterich- 

 thys, though much more depressed. When the arms are flexed by the side the 

 elbow-joint does not quite reach the junction between the anterior and posterior 

 ventro-lateral plates, nor does the apex of the lower arm quite attain to the 

 middle of the last-named body-plate. 



Head. — A large head, minus the extra-lateral plates, is represented in 

 PI. XVII, fig. 1. Unfortunately a large patch of bone is in this specimen broken 

 out behind the orbit, but the detail here lost is supplied in woodcut, Fig. 37, p. 78, 

 from other specimens. 



The median occipital plate (m. occ.) may be described as having seven sides or 

 margins, — one posterior, projecting backwards in a rounded angle, and showing a 

 narrow smooth band overlapped by the anterior median dorsal and the two 

 anterior dorso-laterals ; two lateral, sloping gently outwards and forwards, arti- 

 culating with the external occipital ; two antero-lateral, sloping again inwards and 

 articulating with the lateral plate of each side; and two anterior, which now 

 sloping inwards and backwards form with each other a re-entering angle, which 

 receives the post-median plate in front. The external occipital (e. occ.) is trapezoidal 

 and shows four sides, — one posterior, articulating with the anterior dorso-lateral ; 

 one internal, articulating with the median occipital; one anterior, articulating 

 with the lateral piece (I.) ; and one external, articulating with the angular. The 

 last (ag.) is a very small plate, somewhat oblong in shape, and forms the 

 postero-external angle of the shield. In front of the median occipital, and forming 

 the posterior margin of the orbit, is the post-median (pt. m.), which, irregularly 

 pentagonal, shows one long anterior and slightly convex orbital margin ; two 

 short lateral margins, articulating with the lateral plate on each side ; and two 

 longer postero-lateral ones, which, meeting at an obtuse angle behind, fit into 

 the anterior indentation of the median occipital. 



Bach lateral plate (I.) is of a complicated shape, and consequently difficult to 

 describe, but roughly speaking it may be said to have four margins. The very 



