796 Report OF THE StaTE GEOLOGIST. 
long, slender and nearly vertical crura. The hinge-plate is not 
connected with the lateral portions of the shell, but is supported 
by two slightly divergent, upright lamellae which extend to the 
bottom of the valve; as the valve in this region is deep, these 
lamelle are very conspicuous. The crura widen as they approach 
the apices of the primary lamelle, and form their union with 
these by a short, abrupt lateral curve. The spiral cones are 
approximate, their apices lateral, the ribbon making eight or 
nine volutions in the adult individual. The umbonal blades are 
broad for one-third their length, narrowing abruptly in front 
of the jugum. The jugum is situated posteriorly, and is con- 
structed as follows: Two slender lateral processes are given off 
from the primary lamell, which are directed forward in low, down- 
We 
Fies. 364, 365. Two views of the jugum of Eumetria Verneuiliana, Hall. 
ward curves, and near their extremities turn inward and upward, 
meeting at a point just behind the center of the shell-cavity. 
From their point of union a single process is extended backward 
at an abrupt angle and with a very gentle downward curve, 
terminating just in front of the apices of the primary lamelle 
and above the bases of the spiral cones; its extremity is broad- 
ened and bifurcated, these secondary processes, however, extend- 
ing but a very short distance. The posterior edges of the lateral 
branches of the jugum and of the primary lamelle may be finely 
fimbriated. 
There is usually no trace of a median septum in this valve, but 
occasionally an obscure ridge is preserved. No muscular mark- 
ings have been observed. 
48 
