310 CYPRINID.E. 



crenulation of the inside edge was a sign of maturity, 

 although some conchologists suggested that it might 

 denote a sexual difference ; but the former is opposed to 

 my own observation (especially as regards A. triangu- 

 laris), and no investigation appears to have been made 

 to warrant the latter. Dr. Malm has offered another 

 explanation, by showing that when the margins in the 

 course of growth meet on a rib the inside is notched, 

 but if they meet on a furrow it is plain ; and he observes 

 that the same takes place in species of Murex, which 

 have the inside of the outer lip grooved in perfect ex- 

 amples. To that extent, therefore, the character is 

 correlative with development : but it is exhibited by 

 A. triangularis, which never has any ribs ; I have adult 

 specimens of A. sulcata with the margin quite plain and 

 smooth in front, but distinctly notched on each side ; 

 and A, compressa has always a plain edge, although the 

 shell is ribbed. Some of the cardinal teeth are often 

 rudimentary or so indistinct that, without a close scru- 

 tiny, there appear to be only two teeth in the right, and 

 one in the left valve, which locks into a hollow space 

 between the opposite pair. 



Astarte may be said to be " at home w in the far north. 

 Only two species inhabit the Mediterranean, and those 

 sparingly, while thrice that number abound within the 

 Arctic circle. They frequent sand, more or less mixed 

 with mud, at various depths ; but none are littoral. Many 

 species of remarkable productiveness swarmed in tertiary 

 seas. Fossil shells of that group of Venus which is 

 represented by V.fasciata may easily be mistaken for 

 species of Astarte, some of the characters which distin- 

 guish the latter genus being lost by the removal of the 

 colour and epidermis. 



