Manchestcy Memoirs, Vol. Iv. (191 1), No. 8. g 



giving the appearance of a strongly up-looped 

 ridge, 



(3) A. cygnea type, here the ornamentation resembles 

 U. tumidics, except in that the uploop is far more 

 faintly marked, even ultimately disappearing. 



Umbonal markings are taken as being of some im- 

 portance in the separation of modern species. The genus 

 Pseudanodonta has been founded largely on this. 



L = lime oV S. VeCLifi g^oujft B* B = U tumvfcoLtLS 



6 = GnrourC Lcr>e C -«C PV Cv 



-ye* 



Fio- - 



Diagrams showing typical umbonal markings in ihe British fresh-vvatei 

 Unionidre. 



The British species studied by no means keep to their 

 type. Pictorums, otherwise typical, have been found with 

 markings sometimes resembling and sometimes even 

 identical with those of U. ttnnidus. This latter shows 

 intermediate stages between its own type and U. pictoi'uin 

 on the one hand and A. cygnea on the other. 



Young Anodons collected from the same pond or 

 place on a river show two varieties of markings, with 

 intermediate stages (^Fig. G of Plate). Their ornament 

 may consist of few, well-marked or numerous poorly 



