DONAX. 401 



" Marginales utrinque solitarii, remoti a Cardinalibus, 

 distincti fossula in ipso margine." It is the T. varu 

 abilis of Pulteney, T.depressa of Pennant, Solen pictus 

 of Spengler, T. gari of Poli (but not of Linne), Psam- 

 mobia florida of Lamarck, and T. albida of Dilhvyn (but 

 not of Linne). Leach proposed the generic name of 

 Gobrceus for the present species. 



Sanguinolaria deflorata is a tropical shell, and was 

 wrongly introduced into the British fauna. 



Genus IV. DO'NAX*, Linne. PI. VII. f. 5. 



Body oblong, compressed, rather thick : mantle having a 

 double margin, the outer one of which is clothed with three 

 rows of fringe : tubes not so long as in the other genera, lon- 

 gitudinally lineated ; orifices cirrous. 



Shell wedge-shaped, equivalve, inequilateral, rather solid, 

 mostly smooth and covered with a glossy epidermis, but some- 

 times and partially sculptured by longitudinal striae, some of 

 which are decussated by concentric strire : posterior side ob- 

 liquely truncate : teeth consisting of a double and central car- 

 dinal, with a slight diverging laminar one on either side in the 

 right valve, and two diverging cardinals (representing a re- 

 versed V) with a minute tooth between them at their junction 

 in the left valve, besides laterals on each side of both valves 

 near the beaks : inside having the margin usually more or less 

 notched or crenulated. 



Systematists are not agreed as to whether this genus 

 should constitute the type of a family apart from the 

 TeUinidce. It is bv no means easv to say how many 

 and what kind of characters are essential for the forma- 

 tion of such a group. The animal of Donax resembles 

 that of Psammobia, especially in the ciliated lines of 

 the tubes or siphons ; but the mantle has an outer and 

 inner margin, the former being ornamented with three 

 rows of cirri : the shell is not unlike that of some species 

 * A kind of fish mentioned bv Athena'us. 



