MR. T. ATTHEY ON PTEEOPLAX COENTJIA. 177 



crania, two -well-defined sutures on each have been brought to 

 light, and are seen to divide the bone which had been named 

 postfrontal into three distinct parts, namely, the postfrontal pro- 

 per, the postorbital, and the squamous. 



In the present communication I propose to describe and figure, 

 of the natural size, the upper surface of the smaller and the under 

 surface of the larger cranium, also some ribs and vertebrae, three 

 bones of an extremity, and some scutes, all of which most pro- 

 bably belonged to the same amphibian. 



The crania have undergone immense pressure and are conse- 

 quently much flattened. Together with the other bones they 

 are from the black-shale, a stratum varying from three to four 

 inches in thickness, overlying the Low-Main seam of coal at 

 N'ewsham Colliery, near Blyth, Northumberland. 



Upper surface of the smaller cranium (Plate XV. of natural 

 size and as seen after careful removal of the matrix). — A rib is 

 seen lying along upon the left side of the cranium ; and near its 

 distal end a fragment, which may have belonged to it, partially 

 overlaps the left occipital region; a third piece, the vertebral 

 end of a rib, lies under the fore part of the skull. 



It is worthy of remark that the premaxillary, nasal, prefrontal, 

 and maxillary bones, which naturally form the anteiior end of 

 the cranium, are absent from all the three skulls of Pteroplax as 

 yet known. Such a deficiency has never been met with in skulls 

 of Loxomma or Anthracosaurus The skull of Pteroplax, as wc 

 find it, consists of frontals, parietals, so-called supraoccipitals, 

 postfrontals, postorbitals, squamous, occipitals, cpiotics, and 

 quadrate bones, all firmly united by suture. 



Dimensions. — The skull thus composed measures in length, 

 from the median line in front to the posterior ends of the epiotic 

 horns, six inches and a half, and from the same point to the pos- 

 terior margin of the occiput on the median line five inches. Tlio 

 distance fi'om this last point to the point of the right epiotic horn 

 is very nearly two inches, and that between the points of those 

 horns two inches and nine-tenths. Breadth of the skull at the 

 occipital margin two inches and a half, at the broadest part two 



