ASTEROLEPIS MAXIMA. 



83 



expansion of the articular surface on the outside for the posterior ventrolateral, 

 and extending to the level of the lateral line groove. 



The anterior ventro-lateral plate, of the deep surface of which a natural cast is 

 shown in PI. XVII, figs. 3 and 4, is of a peculiar oblong shape, and consists of 

 two parts ; one broad and horizontal, taking part in the flat ventral wall of the 

 carapace, and another vertical, rising from its outer margin at a right angle, and 

 contributing to the lateral wall. Near the front of this ascending lamina the 

 arm-joint is situated. 



Taking the horizontal part first, it may be described as having four margins. 

 The narrow anterior one is rounded off externally, while from its mesial half a 

 narrow crescentic space is cut out for the semilunar (s. I., woodcuts, Figs. 45 

 and 46). The inner margin is tolerably straight, or slightly convex, and is much 

 shorter than the external one, as the posterior border of the plate, somewhat convex 

 mesially, runs obliquely backwards and outwards to the postero-external angle. 

 The external margin shows near the front a shallow inflexion at the brachial arti- 

 culation, and then proceeds backwards with a gently convex contour. 



Only on the bone of the left side (leaving the brachial joint out of consideration) 

 is an articular area to be observed on the outer surface, and that is along the in- 

 ternal margin (o.), which is overlapped by the corresponding plate of the other 

 (right) side of the body. The latter, the right anterior ventro-lateral, has conse- 

 quently no area on its superficial aspect, as it is overlapped by no other plate. 



Fig. 45. 



Pig. 45. — Restored sketch of the ventral surface of the horizontal lamina of the left anterior ventro- 

 lateral plate, o., articular area for the plate of the opposite side ; b.p., brachial process ; s. I., semilunar 

 plate. 



Pig. 46. — Restored sketch of the deep or upper surface of the horizontal lamina of the right anterior 

 ventro-lateral plate, p., surface overlapping the plate of the opposite side, q., surface overlapping the 

 median ventral ; r., surface overlapping the posterior ventro-lateral. 



The vertical lamina, shown as an impression of the deep surface in PL XVII, 

 fig. 4, rises gradually up from the front, where it is nil, backwards, till at the 



