28 Proceedings of the Royal Physical Society. 



plate of the body on to the external occipital, where it at 

 once bifurcates, a transverse branch passing across over the 

 posterior part of the median occipital to join its fellow of the 

 opposite side. The main groove then runs forward on the 

 lateral cranial plate, and, arriving in front of the median 

 opening, it bends inwards to join the opposite groove on the 

 premedian plate, on which it forms a small backward flexure. 

 This course is altogether similar to that in Asterolejns ; but 

 as we shall see, it is in some particulars different from the 

 arrangement seen in Bothriolepis. 



Body- car ajpace. — This, as already shown by Sir Philip 

 Egerton and Hugh Miller, is nearly quite flat below, high 

 and vaulted above, the sides rising at right angles to the 

 base ; as the former author says, " the contour must have 

 had considerable resemblance to a high-backed tortoise with 

 the carapace culminating near the anterior margin," the 

 transverse section being " not unlike the outline of a stirrup- 

 iron." It is composed altogether of thirteen plates, being 

 two more than the number given by Hugh Miller, but agree- 

 ing in this respect with Asterolepis as described by Pander. 



The general form of these plates is already so well known 

 from the descriptions of Hugh Miller and Egerton, that I 

 need here only allude to certain matters of detail which 

 require correction, some of them, however, being of consider- 

 able importance. In PL I., Figs. 1, 2, and 3, I have repre- 

 sented the outlines of the body-plates as seen from the back, 

 belly, and side respectively, the thick black lines representing 

 overlapping edges, as seen on the external surface, the thin 

 ones those which are overlapped, and which, consequently, 

 are concealed externally when the plates are in sitic^ 



The first point of importance is the presence of two small 

 narrow plates (s. /., Fig. 2), each of which occupies a space cut 

 out from the inner half of the anterior margin of the anterior 

 ventro-lateral {a, v. I.), and is in contact mesially with its 

 fellow of the opposite side. This is Pander's semilnnar in 

 Asterolepis (7, pi. vi., fig. 1), and though not mentioned in 

 the descriptions of Hugh Miller and Sir Philip Egerton, the 

 space which it occupied is distinctly seen in one of Sir 

 Philip s figures (8, p. 305, fig. 2). 



