414 Notices of Memoirs—A. 8. Woodward—on Myliobatis. 
in the absence of a gular plate. On the other hand, the superficial 
bones of the two extinct genera differ greatly from those of Lepi- 
dosteus and closely resemble those of Amia; the peculiar attachment 
of the premaxille in Lepidotus, for example, being reproduced 
almost in every detail in the last-named genus. 
TII.—On toe Dentirion oF A Gigantic Extinct Species oF 
Myrctiopatis FRom THE Lower Tertiary Formation or Heyrt. 
By A. Suita Woopwarp, F.G.8., F.Z.S8." 
\HE Skates of the family of Myliobatide are well known to 
attain a great size, but few examples even of the dentition of 
the largest specimens are preserved in museums. It is, therefore, 
of much interest to record that the British Museum has lately received 
from Surgeon-Captain R. H. Penton a good example of the jaws of 
one of the most gigantic extinct species of Myliobatis, discovered in 
the Lower Tertiary Limestone of the Mokattam Hills, near Cairo, 
Egypt. So far as the present writer is aware, this is the largest 
specimen of the dentition of Myliobatis that has hitherto reached 
any museum. 
The jaws were found in natural association, and the size of the 
teeth is indicated by the followang table of measurements in fractions 
of a metre :— 
Urrrer DENTITION. Lower DeEnTrITion. 
Width of median dental plate... ... 0°13 to 0-135 0°12 to 0-13 
Length _,, . Aw (ON 0-014 to 0-016 
Maximum width of three lateral 
Series Ot gplateshesmt-enmn-cser-enOiO2 0°02 
From these measurements it is evident that the principal teeth 
in the lower jaw are about eight times, those of the upper jaw about 
seven and a half times as broad as long ; while the maximum thick- 
ness of the same teeth in both jaws “equals nearly one-quarter of 
their breadth. These characters, taken in conjunction with the 
form and proportions of the lateral teeth, suffice to distinguish the 
Makattam specimen from the dentition of all known species of 
Myliobatis; and it may therefore be named M. Penton in honour of 
its discoverer. In determining such specimens it is, of course, 
necessary to take into account the mode of growth of the teeth and 
their change in proportion with age; but it does not appear possible, 
in accordance with the ordinary laws of growth, for any known 
type of dentition to develop by increase of size into the one now 
described. The form of the lateral teeth and the transverse section 
of the median teeth seem to be nearly constant at all stages of 
growth in any one species. 
Materials for comparison are unfortunately insufficient to form 
any certain estimate of the size of Myliobatis Pentoni; but if the 
few small examples of the recent Myliobatis aquila in the British 
Museum are at all similar in proportions, the maximum width of 
the disc of the extinct ppecies cannot have been much less than 
five metres. 
1 Abstract of paper read before the Zoological Society, June 20th, 1893. 
