272 Messrs. Hancock & Atthey on Rejptile- and Fish-Remains 



however, from the underside in both specimens, the entire 

 form of this plate is developed. The arrangement and general 

 appearance of the three plates are very similar to those of 

 Loxomma Allmanni figured by Prof. Huxley in the paper 

 already referred to ; only the central plate is not so much pro- 

 duced posteriorly and the lateral ones are much more elongated, 

 agreeing apparently in this latter respect with Archegosaurus^ 

 in which Prof. Owen remarks that the lateral plates " are 

 shaped like beetles' elytra"*. Those oi Pteroplax certainly 

 resemble in form elongated elytra ; but, unfortunately, these 

 plates are not perfect : even in the best-preserved specimen 

 only the posterior extremities are entire ; they are rounded 

 diagonally, the slope being apparently upwards and outwards. 

 What remains of the most perfect plate measures upwards of 

 seven inches in length, and three and a quarter wide. That 

 which seems to be the external margin is thicker than the 

 inner or opposite margin ; and here the surface-sculpture, 

 which is like that of the other bones, is strongest. 



The central plate, which in Labyrinthodonts is usually 

 rhomboidal, is peculiar in form : the two lateral angles are 

 much produced, forming broad rounded lobes or wings 

 (hence the generic appellation) ; their anterior margins have a 

 sigmoidal curve extending to the anterior angle : the poste- 

 rior margin is almost straight, but is a little produced in 

 the centre, where there is a broad flat process extending 

 backwards ; this, however, is not perfect in either speci- 

 men. Here the plate is thickest, and on the surface there 

 is a strong sinuous ridge which extends transversely from 

 side to side, just a little in advance of the posterior margin. 

 When the lateral plates are in their proper position, their 

 posterior extremities would, no doubt, rest against this ridge, 

 the anterior extremities converging forwards. The central 

 plate is upwards of four inches long and six and three-quarters 

 wide. The surface is not sculptured in the usual manner, and 

 must be almost entirely overlapped by the lateral plates. 



The other set of sternal plates is very imperfect ; the cha- 

 racters, however, of the central plate are well developed ; and 

 it fortunately happens that while the right lobe of this plate, 

 in the former specimen, is imperfect, the right lobe of this is 

 quite entire, the other one being injured ; so that, by the aid 

 of the two specimens, the form can be perfectly restored. 



The two vertebrae with the neural arches complete are in a 

 very good state of preservation ; the centrum is quite perfect 

 in one, and almost perfect in the other ; and between the two 



* Palaeontology, p. 179. 



