MTLIOBATID^. 
109 
Family MYLIOBATID^. 
Pectoral fins of very large size, interrupted at the sides of the 
head, but reappearing as one or a pair of small cephalic fins at the 
extremity of the snout. Tail very slender. Cleft of mouth straight, 
and dentition, when present, in the form of a triturating pavement. 
Genus MYLIOBATIS, Cuvier. 
[Eegne Animal, vol. ii. 1817, p. 137.] 
Head free from the disk; so-called cephalic fin single. Teeth 
large, flat, sexangular, tessellated, arranged in seven antero-iwste- 
rior series. The dentition of the upper jaw strongl)’ arched antcro- 
posteriorly, that of the lower jaw quite flat. Dental crown smooth 
or slightly striated ; attached surface of root longitudinally ridged 
and grooved. Except in very young individuals — in which the 
teeth are all approximately of equal size — the median row is rela- 
tively very broad, while the teeth of the three lateral series on each 
side are rarely broader than long. Tail with a dorsal fin near its 
root, generally with a posteriorly situated barbed spine. 
The relative proportions of the median teeth vary with the age 
(or size) of the individual, the breadth gradually becoming greater 
with respect to the length, and in determining the fossil teeth it is 
necessary to allow for this change *. 
Myliobatis dixoni, Agassiz. 
1843. Myliobntis dixoni, X, Agassiz, Poiss. Foss. vol. iii. p. 319. 
1843. Myliobatis heteropleurus, L. Agassiz, tom. cit. p. 323, pL xlvii. 
figs. 6-8. 
18.50. Myliobatu dixoni, F. Dixon, Foss. Suss. p. 108, pi. x. fim 1 2 
_ pi. xi. %. 14, pi. xii. fig. 3. r , r b , , 
1850. Myliobatis contractvs, F. Dixon, op. cit. p. 200, pi. xi fig 17 
Pl- xii. fig. 2. 
(. ) 18o9. Myhobates do Cuise Lamotte, P. Gervais, Pal. Franc. 2nd ed 
pl. Ixvu. lig. 14. 
^^^plTfigl^ H. B. Geinitz {non Agass.), loe. cit. p. 38, 
1888. Myliobatu dtxmi A. S. Woodward, Ann. & Mag. Nat. Hist. [6] 
vol. 1 . p. 41, pl. 1 . figs. 1-4. ° 
1 See Ann. & Mag. Nat. Hist. [6] voL i. 1888, pp. 36-47, pl. i. 
