48 ' Trans. Acad. Sci. of St. Louis. 
hinge line is gently concave, anterior to the beaks the 
shell is imperfect and the characters of the hinge can not 
be made out. Anterior margin regularly rounded from 
the extremity of the hinge line to the basal margin, basal 
margin convex anteriorly but becoming nearly straight 
near the posterior extremity of the shell. A sharp narrow 
ridge extends from the beaks to near the postero-basal 
angle of the shell, its most prominent part descending at 
an angle of thirty-eight degrees with the hinge line. 
Near the beaks the ridge is almost straight and very low, 
but it increases in height as it passes downward and back- 
ward. For the lower two-thirds of its length it is high 
' sharp, and convex upward. Anterior to this ridge is a 
narrow sulcus which begins about three millimeters from 
the beaks and increases in depth and width as it passes 
downward. Posterior to the ridge is a broad sulcus 
slightly arched over by the ridge. On the anterior two- 
thirds of the shell the surface is marked with fine concen- 
tric lines. At the anterior edge of the sulcus in front of 
the ridge these lines meet coarser lines of the sulcus at 
an angle of about eighty degrees. Posterior to the ridge 
short, ill-defined lines descend into a sulcus where they 
meet at a sharp angle lines passing downward and back- 
ward from the hinge line. 
This species differs from Technophorus divaricatus, 
the nearest allied species, in being proportionally much 
broader, in the sulcus anterior to the ridge being nar- 
rower and starting from a point posterior to the beaks, 
in the ridge being sharper, concave upward, arched over 
the posterior sulcus, and forming a greater angle with 
the hinge line. 
This genus has usually been classed with the pelyco- 
pods, but the characters of the hinge are very different 
from those of any known pelycopod and it should proba- 
bly be classed with the bivalve crustaceans. | 
Species based on a single well preserved specimen. 
Number 11551 of the invertebrate paleontological col- 
lection of Walker Museum. — 
