ORDER III PROTREMATA 313 
Stropheodonta, Hall. Shells very much like Rafinesquina, but with the 
cardinal margins finely denticulate and the deltidium flat or not discernible. 
Silurian and Devonian ; North America and Europe. 
Leptostrophia, Hall and Clarke ; Dowvillina, Oehlert and Brachyprion, Shaler, 
are sub-genera of Stropheodonta. Silurian and Devonian. 



Make ali( 
A, Rafinesquina alternata, Conrad sp. Ordovician ; Cincinnati, Ohio. 1/3. B,iR. expansa, Sow.sp. Interior 
of ventral valve, showing muscular and vascular impressions. 
Pholidostrophia, Hall and Clarke. Smooth or squamose, nacreous small 
Stropheodontae. Devonian; North America and Europe. 
Strophonella, Hall (Amphistrophia, Hall and Clarke). Resupinate Stropheo- 
dontae. Silurian and De- 
vonian ; North America and 
Europe. 
Leptaena, Dalman (Lepta- 
gonia, M‘Coy), (Fig. 518). 
Shells having the characters 
of Rafinesquina, but the flatter 
portions of the valves with 
corrugations and wrinkles. Fic. 518. 
Where these cease, the shells Leptaenan vrhomboidalis, Wahlenb. sp. Silurian; Gottland. 
A, B, Dorsal aspect and profile. C, Interior of dorsal valve. 
are more or less abruptly 
and often rectangularly deflected. Ordovician to Carboniferous. 
Cadomella, Munier-Chalmas. Similar 
to Rafinesquina, but in the ventral valve 
between the divergent teeth there is a 
bowl-shaped muscular apophysis for the 
attachment of accessory diductors. The 
prominent socket walls of the dorsal 
valve continued into curved crural 
apophyses, which sometimes terminate 
freely. 
Eee Dae’ Plectambonites, Pander  (Leptaena, 
cof lctermontss transeeragliy, Deb. <p. Silwian} Davidson and auct.), (Fig. 519).  Ordo- 
Te Divaczatesy on Valve Sh. (4, Adductors; vician and Silurian; North America 
and Europe. 
Leptella, Hall and Clarke. Primitive Plectambonites. Upper Cambrian and 
Lower Ordovician ; North America and England. 




