10 
LEPTAENA analogs. 
TAB. DCXV.-/g. 2. 
Spec. Char. Nearly semicircular, with the front 
either straightish or concave, much depressed 
near the beak ; both valves inflated towards the 
front, their margins suddenly deflected ; lower 
valve flat near the beak; surface ornamented with 
diverging striae and concentrically undulated ; 
waves numerous ; hinge-line bent, its area very 
narrow ; beak pointed, hardly projecting. 
Syn. Producta analoga. Phillips, loc. cit. 215. PL 
VII. /. 10. 
This shell grows much larger than the L . clepressa (Tab. 
459) ; its valves are more similar, both being inflated to- 
wards the front, and its outline more rounded ; otherwise 
it strongly resembles it. The area between the valves is 
very narrow. 
It is possible that it may be the L. rugosa of Dalman ; 
but the specimens I have seen from Sweden are most like 
P. depressa , a shell which I believe never occurs above the 
limestone of the Devonian system. Rather frequent in the 
mountain limestone of the North of England and in Ireland. 
LEPTON A distorta. 
TAB. DC XV.— fig. 3. 
Spec. Char. Irregularly orbicular, concentrically 
waved, striated; front generally concave, the 
margin flattened ; hinge-line straight, its area 
triangular ; beak prominent. 
A thicker shell than L. analoga ; well distinguished by 
its projecting beak, very convex valves, which are not com- 
pressed near the beak, and its smaller size. 
I suspect this is P . depressa of Phillips, 215. PI. VIII. f. 
15 ; but as he says he cannot distinguish his specimens from 
P . depressa of the Dudley limestone, I have not ventured 
to quote his name as a synonym. The specimens fig. a. are 
from the Isle of Man, by favour of Mr. Gilbertson. The 
middle figure shows the impressions attributed to the 
ovaria ; similar ones are frequent in casts of other species 
of this genus, especially L. analoga. Fig. 3 b. shows the area 
of the hinge in both valves. It is probably from Scotland. 
It is important to distinguish the two last species from 
L . depressa , which belongs to the rocks of the Silurian 
system, and it may readily be done with a little practice. 
