292 Dr. C. W. Andreivs — Extinct Vertebrates from Egypt. 



It is desirable to give brief preliminary notes on these species, 

 the full description of them being reserved for the monograph on 

 the whole collection which is being prepared. 



MCERITHERIUM GRACILE, Sp.n. 



This species is a smaller and rather more lightly built form than 

 M. Lyonsi. The skull is more elongated in proportion to its width, 

 the palate is narrower, and the squamosal region of the side of the 

 skull is swollen so as to form a slight rounded protuberance, owing 

 apparently to the great development of the diploe in the squamosal 

 and its consequent thickening. The occipital surface also presents 

 some differences from that of M. Lyonsi, particularly in the com- 

 parative narrowness of the escutcheon-shaped plate formed by the 

 supra-occipital and in the smaller extent of the periotic that is 

 exposed. 



The teeth present the most easily recognized peculiarities. The 

 cheek-teeth are much smaller than in M. Lyonsi. They are arranged 

 in perfectly straight lines, the right and left series being almost 

 parallel with one another ; the palate is very narrow. 



The chief points in which the tooth structure is distinguished 

 from that seen in M. Lyonsi are : — 



(1) In p.m. 2 and p.m. 3 the shelf-like surface on the postero- 

 internal border is wanting, and in p.m. 3 at least there seems to 

 have been a distinct postero-internal cusp in its place, but none of 

 the specimens are very well preserved. 



(2) The cingulum is much more strongly developed than in 

 M. Lyonsi, and the enamel is marked by a peculiar sculpture con- 

 sisting of fine irregular vertical fluting. The form and arrangement 

 of the incisors and canines are as in M. Lyonsi. 



The dimensions of the upper teeth are : — 



In M. Lyonsi the length of the p.m. and m. series is approximately 

 160 mm. and of the p.m. series is 74 ; and in the width of the teeth 

 the difference between it and M. gracile is still greater : thus in 

 M. Lyonsi the width of p.m. 3 is 27 mm. and m. 2 27, while in the 

 present species the same teeth measure 20 and 24 respectively. 



McERITHERIUM, Sp. 



The other species is known only by a nearly complete vertebral 

 column, differing from that of M. Lyonsi both in its larger size and 

 in many small structural points. In the absence of any well- 

 preserved remains of the skull and teeth of this form it seems 

 advisable for the present to refrain from giving it a name until 



