LOWER HELDERBERG ROCKS. 
210 
species; and I find that the fossil described by me as Atrypa concinna 
in the Report of the Fourth Geological District (1843), is another species 
belonging to the same group of fossils, in which both the external cha¬ 
racters and internal 'structure differ so essentially from any of the de¬ 
scribed genera of Brachiopoda as to constitute a distinct genus; and 
which, from the general nucleolar character of the known species, I 
propose to designate Nucleospika, 
&EAIJS AUCLEOSPIRl (n. g.). 
[ Gr. •jfvp y|v, nucleus; drfiipa, spira.] 
Shell spheroidal or transversely elliptical, more or less gibbous or ventri- 
cose, furnished with internal spires as in Spirifer : hinge line shorter 
than the width of the shell; cardinal extremities rounded : valves 
subequal, articulating by teeth and sockets. Ventral valve having the 
beak extended beyond the opposite valve, and beneath it a triangular 
depression or area, which sometimes terminates in a shallow spoon¬ 
shaped pit; on each side of which, at the base, is a strong tooth : a 
narrow ridge or septum extends along the centre of the inner side of 
the valve, from beak to base. Dorsal valve furnished with a strong 
spatulate cardinal process, which, rising vertically from the cardinal 
margin, is closely grasped at its base by the cardinal teeth of the other 
valve ; and thence bending abruptly upwards, and expanding, is pro¬ 
jected into the cavity of the opposite beak, lying close upon the under 
side of the false area. This process is grooved or depressed in the centre 
of the upper side, so as to leave between it and the arch of the ventral 
beak a narroAv space for the passage of a pedicle, for the protrusion of 
which a minute foramen is sometimes observed in the beak. From the 
sides of this process, above the junction of the teeth of the opposite 
valve, and at the point where it bends upwards, originate the brachial 
processes which support the spires. A deep cavity beneath the cardinal 
process extends to the dorsal beak, from which originates a thin 
