87 



Species. 

 1. Browniana. 2. contorta. 3. corrugata. 4. subviridis. 



Figure. 



Hyria corrtjgata. PI. 31. Pig. 179. Shell, showing its obliquely tri- 

 angular form, and symphynote- eared growth, with the elongated lateral 

 tooth of the hincce. 



Genus 3. ANODONTA, Bruguiere. 



Animal ; similar to that of Unio. 



Shell ; somewhat obliquely transverse, thin ; hinge without teeth, 

 working only by a prolonged marginal ligament. 



The Anodons are a tribe of Naiads, thin-shelled and toothless, affecting 

 still, muddy waters. The animal is in all respects like that of Unio, the 

 mantle-margins are open in front, giving passage to a large tongue-like 

 foot, and closed behind with two pouting siphonal orifices, the lower of 

 which is invested with a jagged fringe. They are much more numerous 

 in individuals in Britain than the Unios ; but we have only one species. 

 All the Anodons of Europe are, indeed, pronounced to belong to the single 

 species A. cygnea, although it has been described under different phases 

 more than twenty times over. The shell varies interminably, according to 

 the conditions of food, race, and circumstances of habitation, and none of 

 the varieties appear to have any definite limit.* The proportion of Ano- 

 dons to Unios in North America, in respect of species, is about one to 

 eight ; in South America they are nearly equal in number to the Unios ; 

 from Asia we have only eight Anodons as yet, whilst of Unios from that 

 district between forty and fifty have been described ; two Anodons are re- 

 corded from Africa, and one from Australia. 



* " After a wearisome examination of a multitude of forms, both native and foreign, not only 

 must we dissent from the division of this polymorphous bivalve into those numerous species into 

 which it has been separated by the continental writers, but even demur to the possibility of ar- 

 ranging the diversities of shape and colouring into strictly defined varieties, so imperceptibly does 

 one form glide into another, scarcely indicating by any preponderance of peculiarities under which 

 heading it should be ranked." — Forbes and Han/ey, Brit. Moll., vol. ii. p. 156. "The Anodons 

 live in lakes, ponds, marshes, and muddy rivers, crawling slowly on the mud, and leaving a more 

 or less marked groove after them. In the winter, and especially in the summer when the water 

 dries up, they bury themselves in the mud. They feed on decomposed animal and vegetable sub- 

 stances, and the size and solidity of the shell depends on the abundance of the food and the state 

 of quietness or motion and of calcareous matter in the water in which they happen to reside." — 

 Gray, Turton's Man., p. 273. 



