804 Report oF THE STATE GEOLOGIST. 
ment. No trace of the loop has been found, and it is highly 
improbable that a species agreeing in all -known points of 
structure with the spirigerous groups just discussed and having 
also a fibrous shell should possess such a structure. 
(Type, Leptocelia flabellites, Conrad (sp.). Lower Devonian ; 
New York, New Brunswick, Brazil, Bolivia, South Africa). 
Vitulina, Hall. 1860. 
(Plate 39, figs. 28-36.) 
Shell of rather small size ; plano-convex in contour, transverse, 
the hinge-line making the greatest diameter of the valves. The 
pedicle-valve is convex, its umbo scarcely elevated and its apex 
not prominent or incurved. A cardinal area is highly developed, 
and is divided medially by an open, triangular delthyrium, which 
bears no traces of deltidial plates in any condition that has been 
observed. The delthyrium is very wide, its base covering more 
than one-third the extent of the hinge-line. The teeth are blunt, 
thickened, and not supported by dental plates. The scar of the 
pedicle-muscle is distinctly defined, but those of the other mus- 
cles are obscure in their limitation. Under the most favorable 
preservation, there appears a posterior pair, flabellate in form, 
situated just in front of the pedicle-scar, and, more anteriorly, a 
median scar enclosed by two anterior diductor impressions. 
There is, at times, a low median ridge, which is purely muscular 
in its origin. 
The brachial valve is depressed-convex or flat ; it bears a nar- 
row cardinal area coextensive with that on the opposite valve. 
The delthyrium is wide and open, and when the conjoined valves 
are viewed from behind, the cardinal process and socket-walls 
are clearly seen through the wide pedicle-passage. The former 
of these, the cardinal process, is a straight, simple apophysis, 
like that insAnopLorHEca and Catosprra; and the socket walls, 
which are also the bases of the crura, are short, but prominent 
and elevated, bordering deep and narrow dental sockets. The 
brachidium consists of loosely coiled spirals of about four volu- 
tions, the cones having their apices directed toward the lateral 
margins of the valves. On the dorsal side the primary lamella 
are close together, but, on the ventral side, they are wide apart, 
this fact indicating that the bases of the spirals do not lie in 
parallel planes but converge toward the brachial valve, so that 
56 
