382 MANUAL OF THE MOLLUSCAs 
nor foramen? interior of each valve furrowed by two spiral lines 
of four yolutions, directed inwards, and crossing the vascular 
impressions; umbo with three diverging ridges. The small 
ti 
Fig. 186. Produetus? Leonhardi, 2.* 
spiral cavities, once occupied by the arms, and now filled with 
Spar, may be seen in specimens with both valves, by holding 
them tothe light. M. Suess, of Vienna, states that he has found 
traces of yery slender spiral lamelle occupying the furrows. This 
curious little shell most resembles the Triassic Leptena dubia 
(Productus}, Minster (= Crania Murchisoni, Klipst!). 
DAVIDSONIA, Bouchard. 
Dedicated to the author of the Monograph of British Fossil 
-Brachiopoda. 
Type, D. Verneuili, Bouchard. Fig. 187. Devonian, Eifel. 
HA AW 
Dorsal valve, Fig. 187. Ventral valve.2 
Shell solid, attached by outer surface of the ventral valve to 
rocks, shells, and corals; yalves plain, articulated ; ventral 
valye with a wide area (i); foramen angular, covered by a 
conyex 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 yalye, 
* A, translucent specimen; B, interior of dorsal valve. 
