70 PROCEEDINGS OF THE MALACOLOGICAL SOCIETT. 



margin which simulates a posterior lateral tooth. Species occur in 

 the Eocene of America and the Mio(;eue of Europe, and in the latter 

 thev are associated with a true Tivela. 



The hinge of Tivela has been fully described by me in a previous 

 communication,' in which 1 showed that the normal teeth are always 

 present, though they are often crowded into the anterior half of the 

 hinge-plate by the great development of the nyinplial plates. The 

 relationship of Grateloupia was discussed in the same paper. 



Genus Antigona, Schumacher, 1817. 



This genus comprises the shells which Gray regarded as the typical 

 group of the Venus of Lamarck, taiung the type to be Venus verrucosa, 

 but not himself designating it as such.- In this view he was followed 

 by Deshayes (1853) and the Adams (1857), and they all included the 

 genus in the sub-family which possesses an anterior lateral tooth. 

 Homer, however, in 1867 introduced confusion by regarding the 

 group as pfirt of the genus Chione, not even distinguishing it as 

 a separate section, but grouping the species in the same section as the 

 typical Chione under the name of Oniphaloclathrum. Paul Fischer 

 (in 1887) adopted Homer's methdd of classification, and most French 

 geologists have followed in his footsteps, so that even such con- 

 chologists as Cossmann and Peyrot include the Antigona group 

 under a comprehensive Chione genus, though they do separate it as 

 a section under Morch's name. 



In America Dr. Dall has followed the English view of complete 

 generic distinction, and has placed the two genera in separate sub- 

 families. Unfortunately, however, he has revived the abandoned 

 name of Cytherea fr^m Eolten's catalogue, and has applied it to this 

 genus with V. puerpera as a type. Hence, though agreeing with his 

 recognition of the genus, I cannot accept his nomenclature. 



Of course, the wliole question of generic difference depends upon 

 the structural importance of the small tooth on the front pari of the 

 hinge-plate. Homer must have regarded it as a mere excrescence, 

 and not as a definite anterior lateral, though how he could possibly 

 hold such a view with regard to Ant. lamellaris { = A. lamarchi, Gray) 

 is really incomprehensible. The fact is that different species of 

 Antiffona show every gradation between the well-developed laterals 

 of A. lainellaris (in both valves) and the little pustular tooth in the 

 left valve of A. reticulata, which looks like an outgrowth from the 

 anterior cardinal and has no corresponding pit in the right valve. 

 Yet comparison with other species shows tluit the pustule is 

 undoubtedlv an atrophied anterior lateral, apparently in process of 

 being crowded out by a shortening of the hinge-plate and the greater 

 development of the anterior cardinal. 



It may, of course, be argued that the Chione group has been evolved 



' Proc. Malac. Soc, vol. x, p. 266, 1913. 



" See my discussion of the name Venus in Proc. Malac. Soc, vol. ix, 

 p. 242, 1911. 



