382 



MANUAL OF THE MOLLTJSCA, 



nor foramen ? interior of each valve furrowed by two spiral lines 

 of four Tolutions, diroctcd inwards, and crossing tlie vascukr 

 impressions; umbo with three diverging ridges. The small 



Fig. ISO. Productus? Leonhardi, -f-.* 



spn^al cavities, once occupied by the arms, and now filled with 

 spar, may be seen in specimens with both valves, by holding 

 them to the light. M. Sucss, of Vienna, states that he has found 

 traces of very slender s^Diral lamellcc occupying the fuiTows. This 

 curious little shell most resembles the Triassic Leptcena dubia 

 (Productus}, Miinster {=Crama MurcMsom, Klipst!). 



Davidsonia, Bouchard. 



Dedicated to the author of the Monograph of British Fossil 

 Brachio23oda. 



Type, D. Verneuili, Bouchard. Fig. 187. Devonian, Eifel. 



Dorsal valve. 



Fig. 187. 



Ventral valve, r- 



Shell solid, attached by outer surface of the ventral valve to 

 rocks, shells, and corals ; valves plain, articulated ; ventral 

 valve with a wide area (A) ; foramen angular, covered by a 

 convex deltidium {d) ; disk occupied by two conical elevations, 

 obscui-ely grooved by a spiral furrow of 5-6 volutions ; dorsal 

 valve with two shallow lateral cavities ; vascular impressions 

 consisting of two principal sub-marginal trunks, in each valve, 

 * A, translucent specimen ; B, interior of dorsal valve. 



