23 



although only a single specimen exists in the collection, I 

 think it should not be passed over in silence. 



With the hinge characters I am quite unacquainted, the 

 reference to Anoclonta being made purely on external resem- 

 blance. It is, of course, possible that it may^ after all, be an 

 Uiiio, as some species of this genus assume a more or less 

 Anodon-like aspect. 



The 251'esent shell is too wide anteriorly, and the hinge is 

 too horizontal for Z/nio Meyiziesi, G-ray, from New Zealand. 

 It has more the aspect of Zfnio radiatus, Gmelin, but it is too 

 long a shell for this species, and the posterior end too much 

 produced. 



Our fossil approaches some of the flat forms of Anodonta, 

 and it is with these that it must be compared. The more or 

 less compressed valves, strong posterior angulation of the 

 dorsal margin, obliquely truncated posterior margin, and 

 obliquely rounded anterior margin, pending a knowledge of 

 the dental characters of the hinge, all point in this direction. 



Loc. and Jiorizon. — Similar to the first locality of the 

 preceding species (British Museum, Milligan Collection, Reg. 

 No., 96,929). 



DESCEIPTION OF THE FIGUEES. 



Unio Johxstoni, Ethebidge, jnr. 



Fig. 1. Side view of the right valve of an almost complete 

 specimen, nat. size ; Tamar Eiver ; Coll. Brit. Mus. 



Fig. 2. The same specimen seen from the back, showing 

 the hinge, and convexity of the valve ; nat. size. Auodonta 

 Tamarensis, Etheridge, jn. 



Fig. 3. Side view of the right valve somewhat deficient 

 about the posterio-ventral region ; nat. size ; Tamar Eiver ; 

 Coll. Brit. Mus. 



Fig. 4 The same shell showiug the hinge line, and con- 

 vexity of the valves ; nat. size. 



