LOWER HELDERBERG ROCKS. 
SIS 
Fig. 1 c. Enlargement of the beak, foramen and deltidium of the ventral valve, and the 
iipper part of the dorsal valve. 
Fig. If. Dorsal view of a shorter specimen, which has been cnt transversely to show the 
internal spires. 
Fig. 1 g. Enlargement of plications, showing granulose surface and strong imbricating lines 
of growth. 
Fig. 1 h. Surface of plications enlarged, showing granulose surface without imbricating lines 
of growth. 
Geological position and locality. In the shale of the Niagara group, Lockport. 
The illustrations given upon Plate xxvm a comprise all the species of this genus 
which had been positively determined up to the present time. The geological range, 
so far as known, is extremely limited; these species occurring in the Niagara and 
Lower ITelderberg groups only. There are one or two forms in the Upper Helder- 
berg limestones, of which I possess imperfect specimens, which may perhaps come 
under this generic designation; but I have not yet determined their true relations. 
The species described are for the most part of rare occurrence, that of the Niagara 
group being the most abundant; while of T. simplex , I have seen only two speci¬ 
mens ; of T. perforatus , five specimens ; of T. costatus , one specimen, and of T. 
multistriatus, about fifteen; and it should be recollected that the three last named 
are the result of about fourteen years collecting in the Helderberg mountains, during 
ten years of which time several persons were constantly occupied in gathering 
fossils in that locality, many species of which are numbered by thousands of in¬ 
dividuals. 
The T. camura , occurring in the Niagara group, is almost synchronous with the 
first appearance of Spirifer; S. radiatus occurring in the upper limestone of the 
Clinton group, below the Niagara shale, and in the latter rock also in the same 
association with Trematospira. 
TREMATOSPIRA \ Subgroup UllYMOSPIRA. 
Tiie following species were originally referred to Rhynchonella ; but in 
the arrangement of the plates of the third volume some years since, I 
had placed together the three species R. globosa, R. formosa and R. de- 
weyi, believing them to be distinct from true Rhynchondlce. The condition 
of the specimens was such that up to 1856 I had not been able to dis¬ 
cover the internal structure of any of them, and at that time referred 
them with much hesitation to Wa'ldheimia ; and they were so published 
in the Report of the Regents of the University for that year. While this 
