174 



probability caufed many to have been confidered as fmall 

 fpecies of Mytilus, or the fry of larger ; for many fuch 

 Monoculi are capable of fliutting their valves intirely, and 

 inclofing every part of the animal : in which ftate they al- 

 ways are when dead, fo that it is no eafy matter to dif- 

 criminate. 



Mr. Walker is not the only one who has fallen into 

 this error, in his figures 76, 77, and 78, all of which we 

 have received from Sandwich, and have found them in 

 other parts. 



The firfl is found in frefli-water, and is not much unlike 

 Monoculus conchaceus, Gmelin 5)y?. p.3003, but is longer, 

 in proportion to its breadth, than the figure given of that 

 infeft by Donovan, Britijli Infcfls, i. t. 5. 



The other two, given by Mr. Walker, are marine Mo- 

 noculi; both found on Oyjlers, andother rugged (hells; and 

 is not uncommon on the coafl of Devon: efpecially No. 

 77, about the byjfus of the Pinna ingens: both thefe ap- 

 pear to differ only in fhape, and do not feem to have ob- 

 tained a place amongfl; the apterous infefis. When ex- 

 amined under a microfcope, the fhells are punctured all 

 over. 



To thefe fuppofed Mytili of Mr, Walker, we may 

 add the Monoculus conchaceus, which has been fent tc us 

 for fuch ; and we could enumerate many others, which 



inhabit 



