OSTEOGLOSSID^. 
81 
an opposing convex plate of similar structure supported probably 
by the basihyal bone. 
The fragmentary remains of this genus hitherto discovered are 
discussed by the present writer in Ann. Mag. Nat. Hist. [7] vol. iii. 
(1899), pp. 353-361, pis. xiii., xiv. 
Plethodus expansus^ Dixon. 
1850. Plethodus expansus, F. Dixon, Geol. Sussex, p. 366, pi. xxxiii. 
fig. 2. 
O 
1888. Plethodus expansus, A. S. Woodward, Proc. Geol. Assoc, vol. x. 
p. 331. 
1899. Plethodus expansus, A. S. Woodward, Ann. Mag. Nat. Hist. [7] 
vol. iii. p. 354, pi. xiii. figs. 1-4. 
Type. Portion of lower dental plate ; Brighton Museum. 
The type species, of large size, the lower dental plate sometimes 
measuring 0*1 in length by 0'075 in maximum breadth. Lower 
dental plate leaf-shaped, one end being comparatively broad and 
gently rounded, the other end nearly pointed ; its grinding surface 
slightly convex except near the pointed end, where it becomes 
concave; its truncated border more or less tuberculated. Upper 
dental plate nearly as broad as long and regularly concave. 
No bones of this species have hitherto been identified. 
Form. ^ Log. Albian to Senonian : S.E. England. 
(i.) Lower dental plates. 
35369. Fine specimen, described and figured in Ann. Mag. Nat. 
Hist. [7] vol. iii. (1899), p. 354, pi. xiii. fig. 1; Cambridge 
Greensand. Purchased, 1859. 
39103. Broad end of similar plate showing thick bony base, noticed 
ibid. p. 355 ; Cambridge Greensand. Bowerbank Coll. 
35391-92, 35403, 35430. Two large and two small fragmentary 
specimens ; Cambridge Greensand. Purchased, 1859-60. 
P. 1486. Fragment; Cambridge Greensand. Egerton Coll. 
P. 2691. Three fragments; Cambridge Greensand. 
Enniskillen Coll, 
P. 7274-76. Five imperfect specimens, one being very large and 
broad, another displaying the form of the broader end 
Cambridge Greensand. Jesson Coll, 
o 
PAET IV. 
