60 



A 



B 



Figure 41: Right (A) and left (B) valve of the veliconcha of Zirfnaea crispata\ veliconcha 



of Barnea japonica (C). 



26(23). Shell rectangular-oval. Shoulders almost parallel to ventral margin 

 of shell. 



27(30). Anterior margin slightly, tapering. Ligament external. One tooth 

 present at each end of locking line on right valve and a correspond- 

 ing match on left valve. 



28 (29). Shoulders rounded weakly sloping Solenidae, Figure 49. 



29(28). Shoulders straight, appreciably sloping Cultellidae, Figure 50. 



30(27). Anterior margin tapering no more than posterior margin. Ligament 

 internal. Lock consists of row of denticles on right valve and notches 

 on left Cardiidae, Figure 51. 



CHARACTERS OF LARVAE ACCORDING TO FAMILIES 



Mytilidae 



Both ends of the shell are rounded, but the anterior end is narrower than the 

 posterior; the shape of the shell is therefore triangular-oval. The umbo is 

 highly developed. The larvae are fairly large. The hinge line is longer relative 

 to the total size of the shell and, unlike most members of other families, grows 

 in length parallel to the growth of the shell. The hinge has a series of taxodont 

 teeth along the entire hinge line; tooth size increases toward the ends of the 

 row. The ligament is internal and posterior, rarely median. Pigmented spots 

 (eyes) are visible in the veliconcha stage. 



