428 



MOLLUSCA : ACEI'HALA. 



FIG. 652. 



FIG. 651. 



Leda limatula. New 

 England. 



Unio clava, Lam. Reduced. Western States. 



A more recent classification, that of Dr. Gill, in the 

 paper cited on page 406, recognizes five Orders : 



1. DlMYARIA, as Aspergillum, Gastrochcena, Teredo, PJiolas, Solen 



Mya, Pandora, Mactara, TeUina, Cytfierea, Astarte, Cardium, 

 Unio, Leda, etc., etc. 



2. METARRHIPT.E, as Tridaena, etc. 



3. HETEROMYARIA, as Mytilus, etc. 



4. MONOMYARIA, as Pinna, Spondi/lus, Malleus, Pecten, Ostrea, 



etc. 



5. RUDISTA Coral-like moll usks all fossil. 



