368 



MOLLUSCA 



SUB-KINGDOM VI 



byssus passing through a narrow gape between the valves which are otherwise closed. Ordo- 

 vician tfl^evonian. 



The typical Ambonychia, according to Ulrich, is edentulous ; the forms ordinarily passing 



under that name being now referred to Bysson- 

 .ychia. vln this group the byssus does not pass 

 through a notch in one of the valves. 



The Ambonychiidae include the typical mem- 

 bers of Ambonychia, Byssopterla, and Amphi- 

 coelia, Hall ; Opisthoptera (Mega})tera), Meek ; 

 Anomalodonta, Miller ; Byssonychia and Allo- 

 nychia, Ulrich ; and their allies. 



FIG. 619. 



A, Byssonychia, sp. Cincinnati Group ; Cincin- 

 nati, Ohio. Interior of right valve. !/i (after 

 Miller). B, B. radiate (Hall), Ulrich. Same locality. 



Clionychia, Ulrich. 



Byssonychia, Ulrich (Fig. 619). Hinge 

 with several small cardinal and two or three 

 slender lateral teeth ; area striated ; otherwise 

 as in Ambonychia. 



Paleocardia, Hall. Silurian. Mytilarca, 

 Plethomytilus, Hall. Devonian. 



Gosseletia, Barrois (Cyrtodontopsis, Freeh). 

 Thicker shelled, with heavier and more 

 numerous teeth. Devonian. 

 Edentulous, concentrically sculptured. Silurian. 



Family 18. Pinnidae. Meek. 

 Shell Mytiliform, not alate, dimyarian, the anterior adductor smaller; equivalve, 



FIG. 620. 



Pinna pyramidcdis, Miinst. 

 Quader Sandstein ; Schan- 

 clau. 1/3- 



FIG. 621. 



Pinnigena Secbachi, Bohm. Upper Jura ; Kelheim, Bavaria. External 

 and internal views, 1/3 natural size. 



truncate, and wholly open behind; edentulous; area linear; ligament parivincular, 



