212 
PALEONTOLOGY OF NEW YORK. 
The species comprising this group have a very close external resemblance to 
the resupinate shells included under Groups IV, V and VI. There are still 
some differences. In these the hinge-line is shorter, the shells often proportion¬ 
ally narrower, the cardinal area of the pedicle-valve less elevated; the orna¬ 
mentation of the surface is striate but much more finely; the striae are hollow, 
tubulose and produced into short spines, # as in Rhipidomella. 
The interior presents an arrangement of the muscular scars very similar to 
that seen in 0. sinuata and its allies. In the pedicle-valve there is a short 
subquadrate or obcordate area with thickened, elevated margins, and deeply 
sunk in the substance of the shell; in the opposite valve a less distinctly 
defined, quadripartite area. In Schizophoeia, however, the adductor impres¬ 
sion occupying the summit of the median ridge dividing the muscular area 
of the pedicle-valve, is more distinct, the hinge-teeth are more divergent 
and less ponderous; in the brachial valve the crural plates are much less 
divergent and more erect; the cardinal process, which in young'shells, has 
much the same character as in Rhipidomella, becomes absorbed and thus nar¬ 
rowed with age making a thin and sharp ridge; concomitant with this change 
is the formation, in the delthyrial cavity, of one, two or even three minor ridges 
on each side of the original process, so that in old shells the posterior face of 
the process appears to be multilobate. In the very convex brachial valve, four 
(rarely six) deep pallial sinuses take their origin at the anterior margin of the 
muscular area, passing forward as broad, simple, subparallel bands, to near the 
margin of the valve, where they bifurcate and become arborescent. To these 
differences must be added one of distinctive importance, viz., the abundantly 
punctate character of the shell-structure. 
In America the earliest representative of the group is the species here 
described as Schizophoria senecta from the Clinton fauna, this type of structure 
being thus coeval with that of Rhipidomella. In the Lower Helderberg fauna 
is Orthis multistriata, Hall, which is followed in the Corniferous limestone by 
0. propinqua , Hall, in the Hamilton by 0. Tulliensis, Hall, and in the later Devo¬ 
nian by 0. Iowensis, Hall, 0. impressa, Hall, 0. Macfarlanii, Meek, O. Tioga , Hall, 
*See Davidson, British Carboniferous Brachiopoda, pi. xxx, fig-. Id. 
