28 TERMS USED 



almost level with the general surface of the shell, as in 

 Mactra solida. 



Prominens is when the beaks are a little more prominent, as 

 in Mactra stultorum and Vemts undaia. 



Gibbus is when the beaks are swelled out, as in MytUiis Mo- 

 diolus. 



Productior is when they are more extended beyond the surface 

 of the shell, as in Chama gryphoides. 



Corniformis is when they are shaped like a horn, and pro- 

 duced beyond the general svu'face, as in Chama bicornis. 



Fornicatus is when they are arched over, as in Mytilus bilocu- 

 laris. 



Acutus is when the beaks end in rather a sharp point, as Venus 

 Gallina. 



Acitminatus is when the beaks taper to a point like a dart or 

 sting, as in Mytilus eduUs. 



Obtusiis is when the beaks end in a blunt point, like Donax 

 castanea. 



Perforatus is when one of the beaks is perforated, as in Anomia 

 Caput serpentis. 



Secondly, of the Hinge. 

 Cardo, the hinge, consists of the connecting cartilage and the 

 teeth. Linnaeus takes but few of his o-eneric characters 

 from the cartilage, but M. Lamarck has made mvich more 

 use of it ; in many cases it forms a very good generic cha- 

 racter. Many genera have an external cartilage, as for in 



