290 



MR. E. LyDEKKER ON TWO 



larger diameter is placed at right angles to the axis of the jaw. The 

 mandible is readily distinguished from that of Loxomma by the 

 slight development of the sculpture on the outer surface, and also 

 by the great vertical depth of the hinder part of the dentary element, 

 which causes the inferior border of the ramus to assume a highly 

 arcuated contour. 



Having thus briefly sketched the salient features of the teeth and 

 mandible of Loccomma and Anthracosaurus, we may proceed to 

 notice the specimen forming the subject of this part of the present 

 communication. The specimen in question is a slab of shale, 

 exhibiting the external aspect of the greater portion of the right 

 dentary bone of a comparatively large Labyrinthodont from the 

 Lower Carboniferous of Gilmerton ; it is now preserved in the 

 British (Natural History) Museum, where it bears the register- 

 number U. 310, and was formerly in the collection of the late Earl 

 of Eimiskillen. That this jaw belonged to a Labyrinthodont is at 

 once evident from the internal structure of the teeth, as shown by 

 fractured specimens. It is figured on a scale of | in Plate XII. fig. 1. 

 The portion of the dentary remaining is about 8 inches in length 

 and contains a number of teeth, some of which are entire, while 

 others are more or less broken. The jaw is of moderate depth at 

 the hinder portion of the dentary, and thereby approximates to 

 Loxomma^ from which, however, it is at once distinguished by the 

 slight development of the external sculpture ; so that in this 

 respect it is more like Anthracosaurus. At the anterior extremity 

 of the jaw there is the broken base of a large tusk-like tooth*, 

 immediatel}^ followed by an entire tooth of similar type ; then we 

 have an interval of about an inch and a half, occupied by the 

 bases of smaller teeth, which are again succeeded by the stumps of 

 two large tusks. The remainder of the alveolar margin is occupied 

 by a regular series of small teeth, many of which are well preserved. 

 The whole of the teeth have a cylindrical section at the base, while 

 their crowns are smooth, with a convex external and a somewhat 

 flattened inner surface, and there are distinct, although not very 

 prominent, fore-and-aft carinas. Distinct grooves are visible at the 

 base of each tooth, which tend to become obscure as they approach 

 the smooth summit ; and there is a more or less marked tendency 

 to a backward curvature of the summit of the crown ; while each 

 tooth has a large pulp-cavity and strongly marked labyrinthic 

 foldings at the base. 



The above description is quite sufficient to indicate that we have 

 to do with a form which is generically distinct (in the sense in 

 which generic terms are employed in the Labyrinthodonts) both from 

 Loxomma and Anthracosaurus, and therefore from all British Car- 

 boniferous representatives of the Order. Among the numerous forms 

 described by Dr. Fritsch from the Lower Permian of Bohemia, the 

 genus Macromerion'f (or, more correctly, Macromeriam), which was 

 probably allied to Anthracosaurus, presents, however, such a marked 



* These broken teeth are not shown in the figured aspect of the specimen, 

 t Fritsch, ' Fauna der Gaskohle,' etc. vol. ii. pp. 37-4L 



