1862.] HUXLEY — CARBONIFEROirS LABYRINTHOBONTS. 293 



is broken away. In consequence of the projection of this plate 

 beyond the general contour of the skull, the lateral margin of the 

 latter curves suddenly outwards, midway between the orbit and the 

 postero -lateral extremity, and then passes into the straight outer edge 

 of the plate in question. This plate appears to be mainly formed by 

 the quadrate and squamosal bones. Internally it presents a curved 

 contour, convex inwards, which sweeps round when it reaches the 

 posterior margin of the skull, and then passes backwards into the 

 lateral boundary of the epiotic bone. The posterior contour of the 

 skull, consequently, presents a deep notch between the epiotic bone 

 and the plate in question. The epiotic bone, smaU and pointed 

 posteriorly, is wedged in between the supraoccipital element, the 

 parietal, and the squamosal. 



The description here given refers chiefly to the right (proper) 

 half of the skull. The left half is broken away, so as to leave only 

 the left supraoccipital, the left parietal, and part of the left frontal 

 and postfrontal. The complete preservation of the latter bone for- 

 tunately enables one to form an accurate judgment of the minimum 

 width of the interorbital space. 



The structure of the cranial fragment which has been described 

 proves it, without doubt, to belong to a Labyrinthodont Amphibian, 

 and affords sufficient evidence of the character of the whole skull. 

 The straightness of what remains of the external edge renders it 

 probable that the skull was elongated, like that of Archegosaurus ; 

 and on completing the left side of the posterior part of the skull by 

 the aid of the right side, and restoring the general contour on the 

 basis of Archegosaurus, we get a diagram of the whole skull which 

 is probably not very far removed from the truth. 



Posteriorly the skull had a width of 10^ inches ; and if the snout 

 were even less acute than that of Archegosaurus, its total length 

 would be about 14 inches. The largest Archegosaurus skull known 

 does not exceed 12 inches in length. 



From the skull of Archegosaurus, and from that of all other 

 Labyrinthodonts at present known, the present specimen is distin- 

 guished by the proportional size, backward position, form, and 

 veiy oblique disposition of the long axes of the orbits. And as the 

 orbits of species of known genera of Labyrinthodonts do not differ 

 from one another in any essential respect, I conceive this character 

 to be of generic importance ; and I propose the name of Loxomma 

 for the new genus thus characterized. The species may be termed 

 Loocomma AUmanni, after the eminent Professor of Natural History 

 in the University of Edinburgh, who aided me so essentially in dis- 

 covering it. 



The skull, however, was not the first relic of this interesting 

 Amphibian which came to light. What, in fact, originally led me to 

 divine the existence of a large new Labyrinthodont in the Scotch 

 coal-field, was the discovery of a rhomboidal plate of bone so ex- 

 tremely similar to the middle sternal plate of a Labyrinthodont as 

 at once to awaken suspicion. Subsequently I found another speci- 

 men, exhibiting this median plate with the triangular lateral plates, 



x2 



