638 Proceedings. 



structure, and tlie 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 Piastelligera 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 East ellig era, of 

 which there are several species, is limited to the Wairoa series (Triassic), 

 and the Otapiri series (Rhaatic). 



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 pecuharity 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 ;//, 

 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 Ehsetic 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 Ehfetic (Otapiri) 

 series, Athijris 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 

 Sjnrifera. But it differs in the possession of a distinct area and fissure 

 under the beak, and a long, straight hmge-line, in which respect it 

 resembles the Spirifera. Its most obvious peculiarity is that both valves 

 are almost equally convex, and that both are sulcate 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 Spiriferidi^. 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 cut. 



