382 



MANUAL OF THE MOLLUSCA. 



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

 of four volutions, directed inwards, and crossing the vascular 

 impressions; umbo with, three diverging ridges. The small 



Fig. 186. Prodiietus? Leonhardi, f .» 



Spiral 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. Suess, of Vienna, states that he has found 

 traces of very slender spiral lamellae occupying the furrows. This 

 curious little shell most resembles the Triassic Leptcena duhia 

 (Productus;, Miinster {= Crania MiircMsoni, Klipst!). 



Davidsonia, Bouchard. 



Dedicated to the author of the Monograph of British Fossil 

 Brachiopoda. 



Type, D. Yerneuili, Bouchard. Pig. 187. Devonian, Eifel. 



Dorsal valve. 



Tig. 187. 



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, 

 obscurely 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. 



