LOWER HELDERBERG ROCKS. SI 3 



Fig. 1 e. Enlargement of the beak, foramen and deltidium of the ventral valve, and the 

 upper part of the dorsal valve. 



Fig. ly. Dorsal view of a shorter specimen, which has been cut 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 xxviii 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 Helderberg 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. costattis, 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 w^hich 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. 



Trehatospira : SuBaRoup Rhyncospira. 



The following species were originally referred to Rhtnchonella ; 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 Rhynchonella. 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 Waldheimia ; and they were so published 

 in the Report of the Regents of the University for that year. While this 



