103 
of Edinburgh^ Session 1862 - 63 . 
only after having sought in vain for the ventral shields in some 
dozens of specimens that I succeeded in detecting them in a single 
instance. In this case they appeared in a view of the internal sur- 
face of the ventral wall (fig. B) as very minute 'rhombic plates 
lying along the mesial line, where they were interposed between 
the angles of the lateral shields. It is quite possible that the 
ventral plates are more fully displayed upon the outer surface of 
the wall, but in no case did I find this surface sufficiently exposed 
to enable me to obtain a view of them ; while the inner surface, 
on the contrary, was frequently well exposed by the disappearance 
in the fossil of the dorsal shields, and of the series of vertebra-like 
ossicles, which, in the living O^phiuridoe occupies the axis of the 
arms. In most of the specimens sufficiently well preserved to afford 
a view of the ventral walls of the arms, the lateral shields were 
seen to be slightly separated from one another along the ventral 
suture, leaving here a distinct hut narrow fissure, which was not 
interrupted even by the intervention of the minute ventral plates, 
which had in almost every case disappeared. In some instances, 
however, the lateral shields escaped displacement, and the two 
series were then in contact with one another along the line of suture. 
The notch for the exit of the cirri or tentacular ambulacra, situated 
on the aboral edge of every lateral plate, is very distinct, and is 
completed into an entire aperture by the adoral edge of the plate 
next in succession. The spines along the sides of the arms are 
long and slender ; in no case, however, could I satisfy myself that 
more than a single spine was borne by each lateral shield ; but the 
condition of the specimens does not justify our thus limiting the 
number of those spines. Neither was I able to discover in the 
specimens any evidence of scales over the apertures for the cirri. 
The deposit in which Ophiolepis gracilis occurs is a fine dense 
tenacious blue clay of Post-pliocene age. It is situated upon the 
shore of the Firth of Forth, about two miles to the west of Dunbar, 
and is largely worked for the manufacture of bricks. It lies low ; 
and were it not for an artificial embankment, would be flooded at 
high tide. 
In this deposit, at about five feet from the surface, is a horizontal 
bed, where the star-fishes are found. They occur in great numbers 
upon the surface of the bed, which is occasionally separated from 
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