UNio. 33 



tooth, which is also grooved and notched like the double tooth 

 of the right valve into which it locks ; this valve has also a 

 long, sharp and crest-like plate on the posterior side which is 

 morticed into the channel or groove above mentioned : muscidar 

 andpaUicd scars very deep and distinct. L. 1*5. B. 3. 



Var. 1. rad'mta. Shell thinner: epidermis green, marked 

 with divergent yellow rays, which are interrupted by trans- 

 verse narrow zones of the latter colour : posterior side more 

 compressed above: hinge-line nearly straight, especially in 

 half- grown specimens. 



Var. 2. ovalis. Shell triangular-oval, or wedge-shaped, 

 compressed and somewhat incurved in the middle, rather 

 inequivalve in consequence of the right valve slightly over- 

 lapping the other, dark olive-brown : anterior side much 

 broader and abruptly truncate : limide very broad, deep, and 

 oblique. Mi/a ovalis, Montagu, Test. Brit. pp. 34 & 563. 



Habitat : Rivers, canals, and ponds in England as 

 far north as the Went in Yorkshire, and also in South 

 Wales j and it is one of our upper tertiary fossils. Its 

 range extends northwards as far as Finland ; but it does 

 not appear to have been met with south of the Rhone. 

 Var. 1. R. Avon, near Bath (Clark) ; Railway lake near 

 Oxford (Whiteaves). Var. 2. R. Avon, Wilts (Montagu); 

 R. Brent (Metcalfe) ; and from Mrs. Loscombe's col- 

 lection of British shells. The late Mr. Clark also found 

 this variety near Bath, having a green epidermis which 

 is marked longitudinally with yellow rays, and trans- 

 versely with alternate zones of green and yellow. My 

 cabinet contains a specimen of the last variety, Avhich 

 was sent by Col. Montagu to my late friend Mr. Dillwyn, 

 and by the latter presented to me with a few other 

 typical specimens from that excellent British zoologist. 

 The inside of each valve bears, in his well-known hand- 

 writing, the words "Mya ovalis, Wiltshire." This, there- 

 fore, shows what Montagues species really was ; and it 

 is the more interesting because the authors of the ' British 



c5 



