112 CARBONICOLA, ANTHRACOMYA, AND NAIADITES. 
backwards, making an obtuse angle above with the extremity of the hinge-line, 
and below it forms a blunted acute angle with the inferior border, the posterior 
inferior angle being extended far behind the rest of the shell. The hinge-line is 
straight, elevated posteriorly, inclined to the inferior border, so that if each were 
produced forwards they would meet at a very acute angle. It is much shorter 
than the greatest antero-posterior diameter of the shell. The umbones are obtuse, 
swollen, slightly raised above the hinge-line, and not contiguous, and are 
situated anteriorly ; they are not conspicuously marked off from the rest of the 
shell in front, but posteriorly have the upper border continuous with a well- 
marked oblique, more or Jess angulated ridge, which passes downwards and 
backwards to a point somewhat anterior to the posterior inferior angle, becoming 
gradually less marked as it traverses the shell. Anterior to the oblique ridge is a 
well-marked oblique sulcus, which becomes shallower but broader as it approaches 
the inferior margin, which is sinuated at this point. This sulcus can be traced 
nearly up to the umbones themselves. Posterior to and above the oblique ridge 
the shell is rapidly constricted, so as to become concave on the posterior slope, 
above which the valves are compressed and expanded upwards. 
Interiov.—Specimens showing the muscle-scars and hinge-line have not yet 
been obtained. 
Exterior.—The surface of the shell is covered with very fine lines of growth, 
and in the absence of periostracum appears almost smooth. 
The periostracum is thick and very much wrinkled, especially posteriorly, but 
with no definite pattern. The external ligament is almost as long as the posterior 
hinge-margin and comparatively large. 
Dimensions.—The type specimen, Pl. XV, fig. 21, measures— 
Antero-posteriorly. Greatest dorso-ventrally. Laterally. 
25 mm. 14 mm. 15 mm. (but valves are 
somewhat open). 
Pl. XV, fig. 26, 29 mm. 15 mm. 12 mm. 
Localities —Darranpins, Ebbw Vale. Sychffos: Cwm Aman, South Wales. 
Roof of the Hard-mine Coal, and the Cockshead Ironstone, Adderley Green, North 
Staffordshire. 
Observations.—By the kind permission of Sir Archibald Geikie, Director- 
General of the Geological Survey, I have been able to study and figure the 
specimen on which Mr. Salter founded this species which is placed in the Collection 
of the Geological Survey at Jermyn Street, Pl. XV, fig. 21. he shell has the 
valves partially open, and the inferior and posterior borders are incomplete at the 
extreme edge. It is a gibbose shell with very strongly marked oblique keel, and 
the periostracum much wrinkled, but not in quite such a regular fashion as 
depicted in Mr. Salter’s figure. If the right valve be examined it is found that 
