CO^CHYLW—DITHYRJ. 53. 241 



'J iirfon, British Fauna, p. 165. 



hinn. Trans, viii. tab. 3, A. fiof. 3. 



Dorset. Catal. p. 40, tab. 13, fig. 6. 



Diliwyn, Descript. Catal. p. 317. 



Turton, Conch. Diet. p. 116. 

 Musculiis tenuis. Lister, Conch, tab. 153, fig. 8. 

 Mus. nost. In ponds and deep rivers. 



Shell about half the size of the last, covered with a brown or 

 blacUish skin which forms a membrane beyond the margin; the 

 anterior side winged, angular, and somewhat truncate ; the mar- 

 gin opposite the hinge running nearly straight, or slightly in- 

 dented : the space about the hinge always much decorticated as 

 if worm-eaten, like the Lnio raargaritiferus. 



Anouon iestd oblongd depressiusculd, later ibtis rotundatis, Avonensis. 



mnrgine rectinsculo, vmhotiihus stihlenuinalibus. *' 



Shell oblong flattish, rounded at both the sides, with the margin 



nearly straight, and the beaks almost terminal. 

 Mytilus Avonensis. Montagu, Test. Brit. p. 172. 

 Tttrion, British Fauna, p. 165. 

 Linn. Trans, viii. p. 110, tab. 3, A. fig. 4. 

 Tiirfoii, Conch. Diet. p. 116. 

 Mus. nost. From the Avon, in V/iltsliire and Oxfordshire. 



Shell rather less than the last, of an olive brown color, with 

 the front margin nearly straight or slightly arcuated towards the 

 smaller end, and tlie liinge near one end. 



'Ji 



