900 Report oF THE STATE GEOLOGIST. 
Eudesella, Munier—Chalmas. 1880. 
Shells transverse, with long, straight hinge. Cardinalarea and 
deltidium well developed. Pedicle-valve moderately deep; 
muscular scars posteriorand thick- 
ened. Divisions of the internal 
surface corresponding to those of 
the opposite valve. Brachial valve 
flat ; cardinal process prominent, 
subrectangular. Median septum 
extending from the anterior 
Fie. 651. Eudesella Mayalis, Deslong- border to the cardinal region; 
chan C2) ea two shorter lateral septa lie on 
each side. Brachial lamellz following the lobes formed by the 
septa. 
Type, Hudesella Mayalis, Deslongchamps (sp.). 
Distribution. Lias. 
Bactrynium, Emmrich, 1855. 
Synonym; Pterophloios, Giimbel. 1861. 
Shells elongate, plano-convex; attached by the apex of the 
pedicle-valve. Surface smooth or with concentric striz. Shell 
substance punctate. Pedicle-valve highly convex. 
On the interior is a low median septum in the um- 
bonal region. In the brachial valve the cardinal 
process is well developed. The median septum 
begins near the anterior margin of the shell and 
Wie. 652, Bac extends backward almost to the base of the cardinal 
trynium Emm- s Z 
richi, Giimbel. process. On each side are from eight to ten short 
Cems) transverse or convergent septa, together forming 
a series of lobes which are bounded by the brachial lamella. 
Type, Bactrynium Emmrichi, Giimbel (sp.). 
Distribution.  Lias. 
Davidsonella, Munier-Chalmas. 1880. 
Shells small, plano-convex, elongate or subquadrangular; 
attached by the umbo of the pedicle-valve which may thereby 
become deformed or truncated. Cardinal area and deltidium 
well developed. Pedicle-valve with two strong, approximate 
teeth; subcardinal muscular plate divided by a vertical lamella 
152 
