MUSSELS. 37 



they please to the development of another kind of 

 muscle, which is doubtless of greater importance. 



When the water in the Regent's Park was drawn 

 off after the lamentable skating accident in 1867, by 

 which more than fifty persons lost their lives, a very 

 pretty Unio was found partially scattered over the 

 mud. From its shape and iridescent lining, in 

 some specimens tinged with blue or lead colour, in 

 others with pink or champagne colour, it was con- 

 sidered to be a new and undescribed species, and 

 was provisionally named Unio Richensis, after a 

 well-known collector who was the first to call atten- 

 tion to it at a meeting of the Linnean Society early 

 in the following year. Although it has since been 

 regarded by some conchologists as a mere variety 

 of U. tumidus, we think a glance at our figures 

 (PL IV., figs. 1, 2) will show the former opinion 

 to have been not ill-grounded. 



It is a little remarkable that, notwithstanding 

 the depth of black mud in which these shells were 

 found, not a single specimen showed any trace of 

 erosion, although numberless examples of Anodonta 

 cygnea, present in much greater abundance, were 

 considerably eroded, as usual. Another circumstance 



