CARBONICOLA. 43 



In 1881 Professor Koenen gave a good description of the hinge-plate of 

 Lndwig's Unio {Anthracosia) securiformis in the ' Zeitschrift Deutsch Geol. Ges.,' 

 vol. xxxiii, p. 686, as follows : " Die rechte Schale von Anthracosia tragt unter 

 resp. ein wenig hinter dem Wirbel einen dicken, stumpfen Cardinalzalm mit einer 

 oder ein Paar Kanten und darunter eine ganz flache, mitunter gekerbte Einsenk- 

 ung des Schlossrandes ; die linke Schale eine breite, nur wenig gegen den 

 hinteren Schalrand geneigte Binsenkung des hier starker geschwungenen 

 Schlossrandes, und darunter eine Anschwellung desselben, welche allenfalls als 

 schwacher Zahn gedeutet werden konnte. Vorn scheint die rechte Schale iiber die 

 linke iiberzugreifen. Hinten ist, als Seitenzahn deutbar, eine stunipfe 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, 1 

 " It [^Anthracosia] certainly had an internal ligament. 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 striae 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. 



It would seem, from the transverse section of the shell shown on PL 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 Caroonieolm with the Cardinise ; 

 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 Ryckholt referred the Coal-measure Unios to Agassiz's Gardinia, of which genus 

 Woodward 2 considered them to be a sub-genus. Quite recently Polig 3 and Koenen 4 

 have sought to show a close relation between Anthracosia (Carbonicola) and Gar- 

 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 ' Palseontographica,' vol. xxvii, p. 121, 1880. 4 Op. supr. cit. 



