128 



Mr. 0. Thomas. 



[May 16, 



rJiynchus just over a foot in total length, and therefore probably 

 about one-third grown. 



b. That of a young female preserved in spirit, slightly smaller, but, 

 as being a female, in rather a later stage of development than a. 

 This skull is just 65 mm. in basal length. 



Skull a was unfortunately cleaned before any suspicion arose that 

 it was of such special interest, and in the maceration, the teeth, 

 with the exception of those on the left side of the mandible, fell out 

 and have had to be replaced, so that there is a slight element of 

 uncertainty as to their exact positions.* 



In this skull, both above and below, we find on each side twof large 

 and completely calcined teeth (B and C of Mr. Poulton's figures and 

 descriptions), surrounded and separated from each other by a narrow 

 rim of indurated epithelium, which evidently had been (as is proved 

 by specimen 6) continuous with the ordinary lining epithelium of the 

 mouth. Beneath the teeth are separated from the bone by an incom- 

 plete layer of the same material. 



The teeth themselves (Plate 2, figs. 1 and 2) are broad, flat, and 

 low-crowned. The upper ones have each two high, conical, internal 

 cusps, from which minute ridges run downwards and outwards to the 

 outer borders of the crowns, where the edge is peculiarly crenulate 

 rather than cuspidate, in the ordinary sense of the word. On the 

 whole, the anterior and posterior upper teeth are essentially similar to 

 one another, except that the former are narrower, and their outer 

 edges are less markedly crenulated. 



In the lower jaw there is a greater difference between the two. 

 The anterior (fig. 2) is triangular in outline, its longest side is 

 placed antero- externally, and its anterior and postero-external angles 

 have each a high pointed cusp4 ridged on its internal aspect, while 

 the posterior and internal borders are indistinctly crenulated. The 

 posterior fcooth is broadly quadrangular in outline, with a projecting 

 antero-internal angle. As in the corresponding tooth above, there 

 are two cusps on one side, and a series of crenulations on the other, 

 but they are of course reversed, the cusps being external and the 

 crenulations internal. The cusps are high, and connected with 

 transverse ridges running across towards the internal border. The 

 crenulations on the internal border are more numerous in the present 

 specimen than in that figured by Mr. Poulton, there being nine 

 instead of five minute projections. § 



* This doubt is dispelled by an examination of the College of Surgeons specimen, 

 in which the teeth correspond precisely with those of the British Museum skull as 

 now placed.— May 11, 1889. 



+ Three on each side below in the College of Surgeons specimen. — May 17, 1889. 



X These are evidently the two cusps shown commencing to calcify in Mr. Poulton's 

 figure. (Plate II, fig. 16, P>. a.o.o. and p.o.c.) 



§ A considerable amount of individual variation is to be expected in the case of 



