CARBONICOLA. 41 



unfortunately in his earlier publications totally ignoring the work already done in 

 the subject by English, Belgian, and other geologists. The figured specimens 

 are, with very few exceptions, crushed, poor, incomplete, or undeveloped from the 

 matrix — conditions which have not appeared either in the drawings or the text. 

 Not only does he see fit to divide the genus into Unio, Anodon, and Cijrena (Gyclas) 

 without advancing any differential diagnosis, and these genera into many species, 

 but he invents anatomical features in the hinge, and in one case (Anodonta cicatricosa) 

 indicates, in a cast left by the outer surface of the shell, the anterior and posterior 

 adductor-muscle scars, not having recognised that the specimen showed the 

 impression of the external surface only. In another specimen a concretion has 

 been mistaken and figured for a specimen of his Dreissena infiata. 



I examined many specimens, both in Berlin and Dresden, of forms similar to 

 those described by Ludwig, and in no one was I able to satisfy myself of the pre- 

 sence of lateral lamellar teeth ; and, moreover, I felt sure that the species were 

 similar to those which had been described by previous writers. Still it is possible 

 that Professor Amalizky may be wrong in considering that Ludwig meant to 

 describe lateral teeth as being present. In the latter's description of the hinge of 

 his Unio securiformis (G. aquilina), of which the drawings are fairly correct, is 

 found " Das stark entwickelte Schloss besteht aus einem am Vorderende sitzenden 

 gefalteten Zahn und einer runden, langsgefaltteen Leiste oben und nach hinten." 

 The question here arises as to the exact interpretation to be put on the word 

 " Leiste," as to whether it is to be taken as indicating a lateral tooth, or being 

 used to describe the hinge-plate, such a tooth not being present in the specimen, 

 but the posterior part of the hinge being a flattened vertical plate, somewhat 

 irregularly rounded, surmounted by a groove for the insertion of the ligament ; 

 further, in the description of the hinge of Unio Lottneri (Anthracoda acuta) the 

 following expression occurs : — " Das Schloss besteht aus einem dicken, vorsprin- 

 genden, gekerbten Zahne hinter dem Wirbel [anterior], und einer langen, flachen 

 Leiste vor demselben " [posterior]. 



I am inclined to think that what has been mistaken for the posterior lamellar 

 lateral tooth is the upper edge of the flat hinge-plate, which is bounded above by 

 the longitudinal groove for the insertion of the external ligament ; this upper edge 

 of the hinge-plate, being below the level of the superior border of the shell, there- 

 fore becomes apparently very prominent. On this point Ludwig states, " Das 

 Ligament (Schlossband) lag ausserhalb liings der Leiste," which, I think, bears out 

 my view. The hinges of Ludwig's Unio batilliformis, U. crassidms, and U lepidus 

 are pure artistic inventions, and are in the original specimens either very incomplete 

 or partially covered up by the opposite valve. Yet these figures and the descrip- 

 tions are quoted by Professor Amalizky as intermediate forms. 



Considering the great variation of hinge-structure which obtains in a single 



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