CHTMJERIDiE. 
61 
The posterior outer tritor appears to be much more feebly developed 
than in the last-named species, but otherwise the arrangement is 
similar, Many Kimmeridgian fossils, presumably referable to I. 
egertoni , exhibit as much antero-posterior elongation as those placed 
here; and short and long varieties of the mandibular teeth have 
also been observed in other species, e. g. I. thurmanni (/. brevi- 
rostris , Newton). 
Form. Sf Log. Bathonian: Oxfordshire, Gloucestershire, and 
Normandy. 
P. 3106. Left mandibular tooth, described as the type specimen by 
Egerton, loc. cit.; Stonesfield Slate, Stonesfield, Oxford¬ 
shire. Enniskillen Coll. 
P.5150. Imperfect right mandibular tooth, outer aspect; Stones¬ 
field. Egerton Coll. 
28592. Nearly similar specimen ; Eyeford, Gloucestershire. 
Purchased , 1853. 
32545. Right mandibular tooth, forming the type specimen of 
I. tessoni , Agassiz, tom. cit.; Caen, Normandy. 
Tesson Coll. 
41307. Two imperfect pairs of mandibular teeth ; Caen. 
Purchased, 1869. 
44830. Upper portion of small right mandibular tooth ; Caen. 
Presented by Benjamin Bright , Esq., 1873. 
Ischyodus egertoni (Buckland). 
1835. Chimcera egertonii, "W. Buckland, Proc. Geol Soc. vol. ii. p. 206. 
1836. Chimcera egertonii, W. Buckland, Phil. Mag. [3] vol. viii. p. 5. 
1843. Ischyodus egertoni, Sir P. Egerton, Proc. Geol. Soc. vol. iv. 
p. 156. 
1843. Chimcera ( Ischyodon ) egertoni, L. Agassiz, Poiss. Foss. vol. iii. 
p. 340, pi. xl. c. figs. 1-10. 
1871. Ischyodus egertoni, J. Phillips, Geol. Oxford, p. 306, pi. xii. 
fig. 24. 
Type. Mandibular tooth, and the theoretically associated palatine 
and vomerine teeth ; Oxford Museum. 
Mandibular tooth with a deeply sinuous oral margin, acute emi¬ 
nences corresponding to the beak and outer tritors, and the post¬ 
oral margin nearly parallel to the symphysial; beak-tritor narrow 
and elongated antero-posteriorly : outer tritors well developed ; 
median tritor broad, and occupying the greater portion of the 
