APPENDIX TO CHAPTER XII 



191 



ci. Fixed mollusks with large rough 

 shells attached by large valves, 



e 2 - Fixed mollusks, with their pearly 

 shells attached by smaller 

 valve which is flat or concave 

 and perforated or notched 



e 3 . Free mollusks ; hinge line 



straight, formed by ears at 



sides of umbo ; with radial 



ribs ..... 



With many small cardinal teeth in each valve. 



d. With distinct radiating ribs ; shell over 



30 mm. long ..... 



Cs- 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 



Arcidce 



(Ark-shells) 



Nuculidas 

 Ledidce 



KEY TO THE PRINCIPAL GENERA OF FRESH-WATER LAMELLI- 

 BRANCHIATA 



a\. Siphonate ; without marked muscular impression, 



Fam. Cycladidce 

 . Genus Cyclas 

 . , Pisidium 

 Fam. Unionidce 



b\. Valves sub-symmetrical .... 

 62- Valves unsymruetrical ; siphons united . 

 Asiphonate ; with two muscular impressions . 

 &i. Hinge with teeth. 



Ci. With short cardinal teeth and long lateral 



teeth . . . __^ .^- , -. , Unio 



63. With short cardinal teeth and no lateral 



teeth . . .- . ... Margaritann 

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



