CARBONICOLA. 43 
In 1881 Professor Koenen gave a good description of the hinge-plate of 
Ludwig’s Unio (Anthracosia) securiformis in the ‘ Zeitschrift Deutsch. Geol. Ges.,’ 
vol. xxxili, p. 686, as follows: “‘ Die rechte Schale von Anthracosia traigt unter 
resp. ein wenig hinter dem Wirbel einen dicken, stumpfen Cardinalzahn mit emer 
oder ein Paar Kanten und darunter eine ganz flache, mitunter gekerbte Hinsenk- 
ung des Schlossrandes; die linke Schale eine breite, nur wenig gegen den 
hinteren Schalrand geneigte Hinsenkung des hier stiirker geschwungenen 
Schlossrandes, und darunter eine Anschwellung desselben, welche allenfalls als 
schwacher Zahn gedeutet werden kénnte. Vorn scheint die rechte Schale iiber die 
linke iiberzugreifen. Hinten ist, als Seitenzahn deutbar, ee stumpfe Kante auf 
dem Schlossrande der linken Klappe, und in der rechten eine flache Furche vor- 
handen.” There is doubtful mention made here of a posterior lateral tooth, 
which, however, I fail to see in either the figures or the specimen which I had the 
opportunity of examining at Berlin. 
It is difficult to know what King meant by “umbonal ligamental fulcra.” 
He and, later, Salter seem to have supposed that Anthracosia possessed an internal 
cartilage, which occupied a cavity in the hinge-plate; indeed, the latter states,’ 
“Tt [Anthracosia] certainly had an internal hgament. This is shown in a fine 
specimen in the Geological Society’s Museum.” Amalizky combats this statement, 
thinking that the observation must be a mistake. I consider that the striated 
furrow below and posterior to the umbo is for the attachment of the anterior 
and thickened portion of the external ligament, the striz in the hollow in well- 
preserved specimens being due to the continuation of the lines of growth over the 
upper edge of the shell; and this termination of the lines of growth in the groove 
for the ligament occurs all along the edge of the shell. 
Tt would seem, from the transverse section of the shell shown on PI. XI, fig. 2, 
that some cavity was at times left, in which an internal, or the anterior part of 
the external, ligament may have been lodged; and I have returned to this 
question at page 48. 
Many attempts have been made to connect the Carbonicole with the Cardiniz ; 
but it is doubtful whether Agassiz, the author of the latter genus, ever intended to 
include in it the Coal-measure Unios. I have been unable to verify this point, as 
I have been unable to see the original memoirs on the subject. De Koninck and 
de Ryckhelt referred the Coal-measure Unios to Agassiz’s Cardinia, of which genus 
Woodward? considered them to be a sub-genus. Quite recently Polig* and Koenen* 
have sought to show a close relation between Anthracosia (Carbonicola) and Car- 
dinia. The former, however, does not discuss the question of a fresh-water habitat, 
1 «Geol. Survey Mem., Iron Ores of South Wales,’ pt. 3, p. 227. 
2 «Manual of the Mollusca,’ edit. 1, p. 470, 1851-6. 
3 * Paleontographica,’ vol. xxvii, p. 121, 1880. + Op. supr. cit. 
