42 
ACTIXOPTEKYGII. 
P. 2262e, P. 3358. Polished sections of similar rays; from Sands- 
end, near Whitby. Egerton <Sf Enniskillen Colls. 
P. 3356 n. Series of nnjointed rays, the longest piece preserved 0*5 
in length, probably forming the anterior part of the 
pectoral fin. The foremost rays gradually increase in 
length, terminating successively on the anterior border ; 
and the two parallel rods of which each is composed are 
fused together at the pointed distal end. 
Enniskillen Coll. 
Several more imperfect bones of Gyrosteus mirabilis from the 
Enniskillen Collection are also registered under the general number 
P. 3356. 
All the typical examples of Gyrosteus are contained in an 
indurated matrix *; but evidence of a smaller Chondrostean, very 
probably of the same genus, is also found in a soft shale in the 
Whitby cliffs. The following are a few specimens : — 
P. 3357. Hyomandibular 0*18 in length. Enniskillen Coll. 
P. 3356 0. Crushed right clavicle, inner aspect, about 0*1 in depth. 
Enniskillen Coll. 
P. 2262 d. Left supraclavicle, inner aspect, nearly 0*3 in maximum 
depth, differing from that of G. mirabilis in being com¬ 
paratively narrow. Egerton Coll. 
P. 3356 p. Undetermined bone. Enniskillen Coll. 
Family ACIPENSERIDiE. 
Trunk elongate or elongate-fusiform; tail heterocercal. External 
head-bones well developed, those of the cranial roof forming a con¬ 
tinuous shield, which comprises a median longitudinal series of 
azygous elements ; snout prominent and eye far forwards ; mouth 
small, inferior, and suctorial, without teeth in the adult; no pre¬ 
maxilla ; operculum present, but no branchiostegal rays. Squamation 
of trunk comprising few longitudinal series of overlapping bony 
scutes, with irregular intermediate small stellate ossifications; the 
lateral rhombic scales and large fulcral scales on the upper caudal 
lobe robust. 
* This was probably obtained from.the bed immediately above the Jet 
Pock (M. Simpson, Foss. Yorkshire Lias, ed. 2, 1884, p. xiii). 
