CLASS I 



PELECYPODA 



445 



Fjuuily 17. Ambonychiidae Milkr. 



Shell mytiliform, with no anterior wing, the anterior addAictor obsolete ; equivalve, 

 very inequilateral; dentition obsolete or schizo- 

 dont ; ligament external,, multivincular (?) ; 

 byssus passing through a narroiv gape between 

 the valves which are otherwise closed. Ordo- 

 vician to Devonian. 



The typical Ambonychia, according to Uliich, 



is edentulous ; the forms ordinarily passing under , 



that name being now rel'erred to Bijssonychia. In / 



this group the byssus does not pass tlirough a {i 



group the byss 

 notch in one of the valves 



The Ambonychiidae include the typical mem- 

 bers of Ambonychia, Byssoptcria and Amphicoelia 

 Hall ; Ojristhoptcra {Mcgaptcra) Meek ; Anomalo- 

 donta Miller ; Byssonychia and AUonychia Ulrich, 

 and their allies. 



Pig. 60S. 



A, Byssonychia sp. Cincinnati Group; Cin- 

 cinnati, Ohio. Interior of right valve. Vj (after 

 Miller). B, B. radiata (Hall). Same locality. 



Byssonychia Ulrich (Fig. 668). Hinge 

 with several small cardinal and two or three slender lateral teeth ; area striated ; 

 byssal opening present in the upper half of the anterior face ; otherwise as in 

 Ambonychia. 



Paleocardia Hall. Silurian. Mytilarca and Plethomytilus Hall. Devonian. 



Gosseletia, Barrois {Gyrtodontopsis Freeh.). Thicker shelled, with heavier and 

 more numerous teeth. , Devonian. 



Glionychia Ulrich. Edentulous, concentrically sculptured, Ordovician. 



Fig. G69. 



Pinna pyramidalis Miinst. 

 Quader Sandstein ; Schan- 

 dau, near Dresden. 1/3. 



Fig. 670. 



Pinnigena sechaclil Bohm. Upper Jura ; Kelheim, Bavaria. 

 External and internal views, 1/3 natural size. 



