DON AX. 



TESTA transversa, sequivalvis, insequilatera;^ 

 latere antieo plerumque brevi, obtuso. Denies 

 cardinales alterius vuIvcb^ duo, alterius unieus 

 superne bifidiis; laterales, duo vel unus, pl^is 

 minusve remoti. Ligamentum externum, breve, 

 plerumque bipartitum, portiuncula post um- 

 bones posita. Sinus impressionis pallii adhse- 

 rentis musculi, magnus. 



If we except two or three species wliicli Lamarck lias 

 separated from it to form liis present Capsa, and one or 

 two evidently not related to it^ the Linnean Genus DonaT^ 

 has been subjected to fewer curtailments than almost any 

 other : it is nevertheless difficulty on account of the various 

 characters of the hinges of the species included^ to assign 

 to it any definite set of characters^ by which it may at 

 once be distinguished from all others; the shortness of 

 tlie anterior side/' so generally conspicuous, and the 

 rather cuneiform general shape, appear to us to be the most 

 prominent external characters of the species constituting 

 this Genus, although there are not wanting instances in 

 which the sides of the shells are nearly equal, and others 

 in which their general form does not very nearly approxi- 

 mate to that of a wedge. 



* Lamarck is at issue with himself, when he calls the ligament posterior 

 in Donax : for the sake of consistency, we must continue to call the side on 

 which the ligament is placed, as well as the sinus in the muscular impression 

 of the mantle, v/hetheritbe the shorter or the longer, the anterior side. We are 

 av/are that Cuvier has pointed out the impropriety of this ; hut the term anterior 

 is generally adopted for the side which bears the ligament; and posterior for the 

 O|>posite side. 



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