248 Prof. T. R. Jones on the 
up, and nearly always either shortened or lengthened, as the 
case may be, by the lateral pressure to which the rock has 
been subjected. In some pieces of the schist the rough and 
imperfect cleavage gives faces at an angle of about 50° with 
the bedding. 
The casts, however modified in shape, appear to be referable 
to only one species of Leperditia. The original shape seems 
to have been nearly oblong, with almost equally rounded 
ends, equably convex in the middle, and broadly rimmed all 
along the front, ventral, and hind margins. The ocular spot 
and nuchal furrow are generally recognizable. The best pre- 
served of the internal casts is 15 millim. long, and 10 millim. 
high ; another is 20 millim. long, by more than 10 millim. 
high (broken) ; and another 21 millim. long and 13 millim. 
high. The relative convexity of these carapace-valves is 
difficult to determine. ‘There is no trace of radiate or other 
marking on the casts of the valves. 
In the single hand-specimen of limestone from Liebde Bay, 
Spitzbergen, there are several imbedded Leperditia, similar in 
shape to the best of the foregoing from Klaas Billen Bay, 
but not distorted by pressure. ‘Though ‘they retain their shape 
they are, for the most part, too much imbedded to be fully 
seen. ‘The best individual is shown in Pl. IX. fig. 9a. Itis 
10 millim. long by 6 millim. high; and though smaller than 
those in the schist, is probably of the same species. The 
ocular tubercle is higher up in the antero-dorsal region, with 
the nuchal furrow just behind it. Muscular spot not especi- 
ally indicated. Sections of the carapace in the water-worn 
block are shown in figs. 96 and 9c. 
In outline this species from Spitzbergen somewhat resem- 
bles Leperditia Nordenskjeldi, Fr. Schmidt (Mém. Acad. 
Impér. Sc. St.-Pétersb, sér. 7, vol. xxxi. no, 5; Mise. Sila 
ill. p. 25, pl. i. figs. 29-32); but it 1s more broadly oblong, 
being relatively higher, more equally rounded at the ends, and 
it has a broader marginal rim. As this last is very wide, the 
species seems at first sight to belong to Lsochilina; but as 
there is a slight inflection of the ventral edge of one valve 
under that of the other, we must refer it to Leperditia. It may 
be named Leperditia tsochilinotdes. 
2. The Estherie in the carbonaceous shale from Mimers dal 
are all crushed flat on the bed-planes, and are radiately crum- 
pled by the minute folds of the depressed (formerly convex), — 
thin, toughish valves. The black film retains, however, suf- 
ficient indications of the concentric ridge-lines, and frequently 
some trace of the interstitial sculpturing. In shape these 
valves are nearly semicircular, but the curvature hasa general 
