494 
ACTINOPTEKYGII. 
P. 4300. Another slender flattened rostrum, smaller and showing 
two longitudinal canals ; London Clay, Sheppey. 
Enniskillen Coll. 
P. 9483. Acuminate end of flattened rostrum; London Clay, 
Sheppey. History unknown. 
Genus ACESTRUS, novum. 
[CoV Agassi 25 MS., Rep. Brit. Assoc. 1844 (1845), p. 308.] 
A genus known only by the hinder portion of the cranium, 
considered by Agassiz to belong to a fish of the family Xiphiidse. 
Cranium flattened and depressed, the sides of the roof slightly 
sloping downwards and outwards ; the three pairs of fossm for the 
forward production of the lateral muscles of the trunk extending to 
the frontals, which are large and ornamented with conspicuous 
radiating smooth ridges. 
Acestrus ornatuS) sp. nov, 
[Plate XIX. fig. 3.J 
1845. Acestrus ornatus, L. Agassiz, loc. cit. p. 308 (name only). 
Type. Hinder fragment of cranium; British Museum. 
The type species, with cranium as much as 0*075 in diameter at 
occiput. Special characters of roof shown in the figure. 
Form. ^ Loc. Lower Eocene (London Clay) r. London Basin. 
P. 627. Abraded fragment of hinder part of cranium, labelled by 
Agassiz and marked by Egerton as interrded to be the 
type specimen ; Sheppey. Egerton Coll. 
P. 1739. Larger specimen, well preserved but partly pyritised, 
shown from above of the natural size in PI. XIX. fig. 3; 
Sheppey. The epiotics {ep.o.) are relatively large and 
prominent; the exposed ornamented portions of the 
supraoccipital (s. occ.), parietals (p«.), and squamosals 
{sq.) are comparatively small. The ornamentation of the 
large frontals (/r.) is well shown. The postfrontal or 
sphenotic projects outwards a little on each side. 
Egerton Coll. 
P. 1739 a. Imperfect hinder half of very small skull; Sheppey. 
Egerton Coll. 
