JUKES-BROWNE : DOSIXIA AND ITS SUBDIVISIONS. 101 



that it further resembled Dosinia in the thickness of the hinge-plate, 

 in the rugosity of the anterior lateral tooth, and in the manner in 

 which the right posterior cardinal springs from the end of the incurved 

 anterior margin. It also agrees with Dosinia and with Aphrodina in 

 the forward direction of the right anterior cardinal, which in Pitaria 

 and in typical CaUista is more directly transverse, and nearly parallel 

 to the middle cardinal. 



M. Cossmann, writing in 1909,' differs from me with regard to the 

 affinities of this species, and remarks as follows (in French, which 

 I translate): '^ Cordiopsis evidently belongs to Meretrix by its form, 

 by its smooth surface, without a carinated escutcheon, and especially 

 by the small tooth A ii [the anterior lateral], which is always isolated 

 from2«" [the anterior cardinal]. He distinguishes it from Pitaria 

 " by the disposition of its cardinal teeth, the form of its sinus, by its 

 ranch more cordiform shape, and by the disappearance of Ai and An. 

 He further remarks : On the other hand, it seems to us impossible 

 to connect it with Dosinia, which is a genus well diiferentiated by its 

 orbicuUir and flattened form, as well as by its narrow and pointed 

 sinus, by its impressed lunule, by its grooved surface, etc." 



jS^ow the characteis by which he connects Cordiopsis with Meretrix 

 are of no value whatever, for Venus incrassata is not absolutely smooth 

 and glossy like Meretrix and CaUista, but is finelj- concentrically 

 striated like Pitaria and many Dosinice. Again, the anterior latei'al 

 tooth of V. mcrassata is pustular and tends to disappear with age, as 

 in some species of Dositiia, whereas in Meretrix and CaUista it is 

 elongate, tall, and persistent. 



Moreover, the points by which he tries to distinguish Cordiop>sis 

 from Dosinia show that he does not at all understand the real 

 characteristics of that genus, the shells of which are not always 

 flattened, the sinus is not always narrow and pointed, nor is the 

 lunule always impressed. It is clear, in fact, that M. Cossmaun's 

 principles of classification differ from those of most modern con- 

 chologists in that he regards the external char.icters of the shell and 

 the form of the pallial sinus as being of equal or greater importance 

 than the characters of the liinge. I adliere to the prevalent view 

 that the latter afford a much better and more constant criterion 

 for distinguishing genera and sub-genera from one another than 

 any other feature in Lamellibranch shells. 



Comparing the type of Cordiopsis witli that of Sinodia he says, 

 " the contour of the hinge-plate is much more excavated and sinuous 

 in C. incrassata, which when of the same size has a more remote 

 (posterior lateral) tooth 33, and a much deeper pit to receive An, 

 with two protuberances (A i and A in) which are not so noticeable 

 in Sinodiay ... " The polymorphic ontogeny of Cordiopsis, its 

 cordiform aspect at all ages, its less developed and narrower sinus, 

 make it certain that we cannot confuse it with Sinodia, if we do not 

 rely exclusively on the single criterion of the hinge in the classification 



' " Conchologie Neogenique de I'Aquitaine " : Actes Soc. Lin. Bordeaux, 

 t. Ixiv, p. 387, 1910. 



