2 DK. A. SMITH WOODWARD ON THE [vol. lxxv, 



along the plane of the mouth, so that the dentition of each is 

 exposed from the oral aspect, as shown in PL I. Of the carti- 

 lages only fragments remain behind and partly below the teeth, 

 especially in the wider of the two jaws (which is here regarded as 

 the upper). Nearly all the teeth seem to be present in the narrower 

 or supposed lower jaw ; but some, of the small anterior teeth are 

 broken away from the front of the opposing jaw, and a few 

 of these are seen adhering to the matrix behind the ' lower ' sym- 

 physial dentition (PI. I, fig. 3, a?). Sufficient points of contact are 

 preserved between the two slabs, to show that in fossilization the 

 narrower jaw was pushed a little forwards beyond the wider jaw. 



The teeth are closely arranged in antero-posteriorly directed 

 series, interlocking by alternation, and most of them must have 

 been borne on a very stout symphysis. Only the outer paired series 

 extends farther backwards over the ramus of the jaw. At the back 

 of the symphysis, the one jaw is not much wider than the other ; 

 but behind this the narrower dentition shows a marked constriction, 

 and its paired outer series of teeth extending over the mandibulai 

 rami, as preserved, is much less divergent than the corresponding 

 series in the wider dentition. There may be some displacement by 

 crushing. 



In the wider dentition (PI. I, fig. 1), which by reference to 

 Janassa hituminosa may be regarded as upper, the teeth at the 

 back of the symphysis much resemble those from the Carboniferous 

 Limestone of Derbyshire named Glimaxodus imhricatus by McCo}^. 1 

 They are in three antero-posterior series, one median and one 

 paired, and those of two transverse rows seem to be about equal in 

 size. The concave hinder face of the crown in these teeth is nearly 

 as deep as wide, tapering rather rapidly to a bluntly-rounded apex, 

 of which the roughened surface evidently denotes wear during life 

 The base-line of the crown descends in the middle almost in the 

 shape of a loop, and it is marked by five concentric imbrications, 

 of which the upper two are more widely spaced than the others. 

 Though antero-posteriorly compressed, as usual, the dental crown 

 is moderately thick, and its convex anterior face is shown to have 

 been of very little depth, the basal imbrications in one broken 

 tooth being visible not far below the apex. Except in a small part 

 of the anterior face, which is dense (and black in the fossil), the 

 whole of the crown consists of highly-vascular dentine (white in 

 the fossil) traversed by large vertical canals. So far as can be 

 determined from the broken remains, the three teeth of the next 

 (or third) transverse row forwards are nearly similar to those just 

 described and not much smaller, but in them the highly- vascular 

 dentine forms only the core of the crown. The root is obscured 

 in all these teeth. Farther forwards there are fragments of much 

 smaller teeth, of which three examples in one transverse row are 



1 F. McCoy, in Sedgwick & McCoy, ' British Palaeozoic Bocks .... & 

 Fossils,' London & Cambridge, 1855, p. 620 & pi. iiia, fig. 5; A. S. Woodward, 

 Catal. Foss. Fishes Brit. Mus. pt. i (1889) p. 38 & pi. i, figs. 1-2. 



