522 Mr. Owen on species of 



jaw last described, that they must be regarded as belonging to the same species. 

 There are not less than fifty sockets in a single linear series, and at the anterior 

 inflected part of the jaw is the base of the socket of a large tooth six lines in dia- 

 meter ; the serial teeth gradually diminish in size toward the anterior portion of 

 the jaw ; the posterior teeth, which are slightly compressed at their base, in the 

 antero-posterior direction, present here about a line and a half in diameter ; the 

 anterior ones half a line across the same part ; the length of some of these small 

 anterior teeth above the sockets is three lines, they are terminated by subacute 

 extremities ; the sockets do not lie between parallel lines ; the alternate ones are 

 placed a little more internally. The teeth were present chiefly in the more exter- 

 nal sockets ; but where they remained in both, the row of teeth presented the same 

 slightly zigzag disposition. Owing to the circumstance of the anterior part of the 

 jaw having been broken, it cannot be determined whether any of the smaller or 

 serial teeth were continued external to the large anterior tusks, — a remarkable ich- 

 thyic character which I shall have to notice in a subsequent fossil. The sockets of 

 the teeth are as shallow in the present as in the preceding fossil ; the outer wall is 

 more developed than the inner, and the anchylosed bases of the teeth more nearly 

 resemble in their oblique position those of the existing Batrachia. The teeth are 

 directed slightly inwards, and are probably received within the series of the upper 

 jaw when the mouth is closed. The striation and fluting is confined to the basal 

 third of the tooth, as is also the labyrinthic inflections of the external cement. 

 Above this part the dentine consists of fine calcigerous tubes, radiating from the 

 linear remains of the pulp-cavity at right angles to the surface of the tooth ; being 

 parallel with the axis of the tooth where they form its apex, and gradually inclining 

 outwards until they become transverse to that axis, which is their disposition in 

 the b^dy of the tooth, between the apex and the commencement of the inflected 

 vertical folds of the cement. Beyond this part, therefore, the tooth of the Laby- 

 rinthodon resembles, in the simplicity of its intimate structure, that of the entire 

 tooth of the ordinary Batrachia and of most reptiles. The vertical inflected pro- 

 cesses of the cement are at first short and straight, occurring at pretty regular 

 distances around the circumference of the tooth ; so that here the tooth partakes 

 of the structure which I have before described as characterizing the base of the 

 tooth of the Ichthyosaurus. Soon, however, the primitive inflected folds of cement 

 sink, deeper into the dentine and commence their undulating course ; other pro- 

 cesses, at first simple like the preceding, begin to penetrate the dentine at the in- 

 terspaces of the primary folds ; these begin to take on a sinuous course a little 

 nearer the base of the tooth ; and a transverse section at this part exhibits the 

 modification of the labyrinthic structure exhibited in the woodcut, fig. 2, p. 511. 

 The long and slender character of the maxillary ramus, suggesting the name of 



