119 



a small opening for the passage of the foot. Why then, it may be asked, 

 have we not reconstructed the subdivision of this Order into families? 

 Many changes will have to be made in the method of classification adopted 

 in this work as the animals become known. At present little is known of 

 the malacological characters of the genera of this family except by their 

 British representatives, and the proportion of these to the foreign species, 

 known only by their shells, is small indeed. The strongest conchological 

 characteristic of the genera consists in the posterior or siphonal end of the 

 shell being more or less attenuated by an angular depression which radiates 

 from the umbo and is sometimes flexuous. 



Donax. Tellina. Capsa. 



Iphigenia. Galeomma. Capsella. 



lucina. psammobia. soletellina. 



CORBIS. PSAMMOTELLA. SaNGUINOLARIA. 



Genus 1. DONAX, Linnceus. 



Animal ; oblong, its mantle f reel?/ open in front, with fringed, or 

 partially fringed, margins ; siphons comparatively short, diver- 

 gent, the branchial siphon with pinnated cirrhi around its ori- 

 fice, the anal with simple denticulations ; foot large, apiculated, 

 sharp edged. 



Shell ; triangularly ovate or oblong, more or less wedge-shaped, 

 sometimes flexuous, equivalve ; hinge composed of two cardinal 

 teeth in one valve, and one in the other ; bifid at the upper part, 

 two, or one, more or less distant lateral teeth in each valve. 



There is scarcely any assemblage of bivalves so distinct in their generic 

 character as those which have been associated without change since the 

 time of Linneeus under the head of Donax. As in most of the Nymphacea 

 the animal has its siphons separated to the base ; but in Donax they are 

 rather short, and there is a peculiarity in the margins of the orifices, one 

 being pinnately cirrhated, the other simply denticulated. In Tellina the 

 margins of the siphonal orifices are plain, or, at least, very indistinctly 

 denticulated. There are more characteristic distinctions in the shell of 

 these mollusks than in the soft parts ; in Donax the shell is typically of a 

 triangular wedge-shape, the anterior side being long and rounded, the 

 posterior very short and abruptly truncated, and of rather solid growth. 

 They have, with rare exception, little sculpture, and they present a strong 

 uniformity of colour, a fulvous or dull grey, frequently tinted with rays. 



