576 MOLLUSCA 



partitions, the ascending limb of the outer leaflet being united with the 



mantle; genital glands have independent openings to the outside; two 



adductor muscles usually present; mantle edges more or less fused and 



the siphons present (Fig. 888), either in form of closed tubes or not; 



foot usually large, with byssus little or not at all developed: about 27 



families, grouped in 7 suborders, including most pelecypods. 



Key to the suborders of Eulamellihranchiata : 



Ci Mantle often below, shell usually with no pallial sinus 1. Submytilacea 



Oa Shell usually thin, with paHial sinus (Fig. 880, 10) ; siphons usually 

 present. 

 &i Pallial sinus prominent. 



Cj Pallial sinus extending far forwards 2. Tellinacea 



Ca Pallial sinus not so large. 

 di Animals do not bore in solid objects. 



€i Shell thick and solid and more or less round 3. Veneracea 



€2 Shell rather thin and usually elongate 5. Myacea 



dj Animals bore in clay, wood, or rock 6. Pholadacea 



5j A slight pallial sinus or none present. 



Gi Shell thick, usually ribbed 4. Cardiacea 



Ca Shell thin 7. Anatinacea 



Suborder 1. SUBMYTILACEA. 



Mantle edges open below; closed siphons and pallial sinus usually 

 absent; 2 add-uctor muscles; cardinal and lateral teeth (Fig. 889) well 

 developed : about 16 families, in fresh and salt water. 



Key to the families of Submytilacea here described: 



Oi Animals marine. 

 61 Shells not minute, although in some cases small. 



Ci Shells radially grooved 1. Carditidae 



Ca Shells not radially grooved. 

 di Umbo not at forward end. 

 ei Lunule present (Fig. 889, 4). 

 /i Adductor muscle impressions nearly equal in size. 



Qi Shell mostly more than 20 mm. long 2. Astartuiae 



<72 Shell mostly less than 8 mm. long 3. Crassatellidae 



/a Anterior muscle impression much the hmger 7. Lucinidae 



ei Lunule absent 4. Cyprinidae 



da Umbo at forward end (>. Dreissensiidae 



Z>2 Shells minute. 



Ci Ligament external 8. Kellyellidae 



Ca Ligament internal 9. Erycinidae 



Oa Animals in fresh water. 



\ Shell large 5. Unionidae 



5a Shell minute \. 10. Cyrenidae 



Family 1. CAEDITIE^AE. 



Shell heart-shaped or ovate, with radiatii^g ribs or striations, hinge 

 thick, with 1 or 2 cardinal and 1 or 2 lateral teeth ; foot with byssus ; no 1 

 closed siphon: about 10 genera, all marine. 



