APPENDIX TO CHAPTER XII 



191 



]_. Fixed mollusks with large rough 

 shells attached by large valves, 



'2- Fixed mollusks, with their pearly 

 shells attached by smaller 

 valve which is flat or concave 

 and perforated or notched 



e*. Free mollusks ; hinge line 



straight, formed by ears at 



sides of umbo ; with radial 



ribs ..... 



With many small cardinal teeth in each valve. 



Ci. With distinct radiating ribs ; shell over 



30 mm. long 



Co. Smooth, length and height equal ; under 

 12 mm. long 



c 3 . Elongated shells, length nearly or twice 

 height ; a pallial sinus .... 



Ostreidce 



(Oysters) 



Anomiidce 



(Jingle shells) 



Pectinidce 



ArcidoK 



(Ark-shells) 



NucnlidcK 

 Ledidce 



KEY TO THE PRINCIPAL GENERA OF FRESH-WATER LAMELLI- 



BRANCHIATA 



i. Siphonate ; without marked muscular impression, 



Fain. Cycladidce 

 bi. Valves sub-symmetrical ..... Genus Cyclas 



b>2- Valves unsymmetrical ; siphons united . . Pisidium 



cto. Asiphonate ; with two muscular impressions . Fain. Unionidw 

 l)\. Hinge with teeth. 



Ci. With short cardinal teeth and long lateral 



teeth ....... Unio 



Co. With short cardinal teeth and no lateral 



teeth ....... Maryaritana 



Hinge without teeth, or with only a small ridge, Anodonta 



