91 



tremely thin that the centra! and fmalier lateral teeth are 

 not fo readily difcovered. 



The animal of this, as well as the two preceding, are 

 viviparous, producing from fix to twelve at a time, and 

 are probably either androgynous or hermaphrodite, as all 

 thofe we have differed in the early part of the month of 

 June contained perfeft young. It is a Tethys, of a pellucid 

 white colour, with a very long tongue-fhaped foot, or 

 fuJlentaciUum, fituated at the pofterior end, exceeding the 

 length of the fhell when extended ; by this it moves back- 

 wards by jerks, dilating and contrafting it ahernately : 

 at the anterior end are two tubes clofe together, the longeft 

 is neareft the hinge, and is about one-fourth the length- 

 of the fhell. 



N 2 GEN. 



