PALAEONTOLOGY OF NEW-YORK. 
The following figures are illustrations of one of the typical species of Rhyx- 
CHOSPira, from the Lower Helclerberg group. 
RHYNCHOSPIRA FORMOSA. 
1 & 4 2 3 5 6 
Fig. 1. Dorsal view, natural size. Fig. 2. Interior ot a dorsal valve, showing the cardinal process, etc. 
Fig. 3. Profile of figure 2, showing the recurved cardinal process. 
Fig. 4. The ventral valve of the same species. 
Fig. 5. A longitudinal section, showing the articulation of the valves, the origin of one of the crura, 
the spire, etc. 
Fig. 6. The upper part of two valves, showing the mode of articulation. 
Gems NuCLEOSPIRA* (Hall). 
This genus was proposed by me to include a few small species of fos¬ 
sils which had heretofore been referred to Spirifer, Atrypa, Orthis, etc., 
but which do not possess the true characters of either of these genera. 
Since we know the peculiarities of its internal structure and the accom¬ 
panying exterior, together with the punctate texture, there is no longer 
.any difficulty in recognising these shells among the other Brachiopoda. 
The following are the important characters of the genus, as determined 
from the examination of the species'of the Niagara, Lower Helderberg 
and Hamilton groups. 
Shell depressed spheroidal or transversely elliptical, more or less, 
gibbous or ventricose, furnished with internal spires as in Spirifera ; 
hinge-line shorter than the width of the shell; cardinal extremities 
rounded : valves subequal, articulating by teeth and sockets. Ventral 
valve having the beak slightly extended beyond the opposite valve, and 
beneath it a triangular depression or area, which has sometimes a 
shallow semispoonshaped form; on each side of which, at the base, is a 
strong tooth. A narrow ridge or septum along the centre of the inner 
* This genus was first described in the third volume of the Palaeontology of New-York, p. 219, and 
is copied on pages 24 and 25 of the Twelfth Report on the State Cabinet. 
