538 Proceedings. 
structure, and the internal casts show that a strong septum divided the 
prominent ventral beak into two cavities. 
A third form related to Spiriferina in having a punctate shell-structure, 
differs so essentially as to require separation as a genus, to which the 
name Rastelligera has been applied, from the peculiar character of the. 
hinge-line, which is enormously long in proportion to the height of 
the shell, and along the hinge-margin both valves are minutely denti- 
culate, with rake-like teeth that appeared to interlock. The proper 
dental processes are only feebly developed, if not altogether absent, 
. and both valves are nearly equally convex. The genus Rastelligera, of 
which there are several species, is limited to the Wairoa series (Triassic), 
and the Otapiri series (Rhetic). 
The next form, which is like Spiriferina in general outline, although 
in different species it varies greatly in the extension of the hinge-line, 
has a marked peculiarity in the arrangement of the dental plates, 
which spring from the sides of the mesial septum, so that a horizontal 
section of the beak, or the fissures seen in the natural internal cast, show 
the interior processes to have been arranged like the Greek character V, 
from which the name Psioidea has been given to the genus. Some of 
the species are remarkable for the great development of a concave triangular 
area, overhung by a strongly projecting dorsal umbo. This genus has been 
discovered in the Silurian formation, and finally disappears in the upper 
part of the Rhetic beds. 
Besides the above, which are all allied to Spiriferina, true forms of 
Athyris (Spirigera) are not uncommon from the Triassic formation down- 
wards; but in the same formation, and in the overlying Rhetic (Otapiri) 
series, Athyris is only represented by an allied genus, having also a 
lamenellate shell-structure, but possessing characters that have required 
its separation under the generic name of Clavigera. 
This form agrees with Athyris in having the ventral beak foraminate 
and in the apices of the spire-cones being central and directed to the 
middle of the lateral margins, and not to the cardinal angles as in 
Spirifera. But it differs in the possession of a distinct area and fissure 
under the beak, and a long, straight hinge-line, in which respect it 
resembles the Spirifera. Its most obvious peculiarity is that both valves 
are almost equally convex, and that both are suleate in the median line, 
and that both a foramen and a fissure are present in the ventral valve, which 
is a most exceptional character among Spiriferide. The name has been 
given on account of the strong stud-shaped cardinal boss, which in the 
cast gives rise to a singular hood-like process, owing to the matrix that 
lodged between the interior surface of the dental-plates and the boss having 
been preserved after the shell has weathered out. 
NS see ee 
