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 less 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. 



Interior. — 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). 

 PI. XV, fig. 2(3, 29 mm. 15 mm. 12 mm. 



Localities. — Darranpins, Ebbw Vale. Sychffos : Cwm Aman, South Wales. 

 Hoof of tho 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, PI. XV, fig. 21. The 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 



