28 



[Assembly 



The species positively determined to tlie present time are from the rocks 

 of the Lower Helderberg group ; to which may be added the Trematospira 

 {Atrypa) camura of the Niagara group, which presents some slight devia- 

 tion in the perforation of the beak, and a species from the Hamilton group 

 which is apparently of the same genus. 



Fig. 1. Trematospira costata. Dorsal and front views. 



Fig. 2. T. perforata. Dorsal view. 



Fig. 3. T. multistriata. The ventral valve, from which the dorsal valve has been 



ground away, showing the spires as they appear on the polished surface of 



the stone. 



Fig. 4. Ventral and front view of T. multistriata. 



Geological range. Admitting the species from the Hamilton group as of 

 the same genus, its range is from the Niagara group to the Hamilton group, 

 or from near the base of the Upper Silurian to the middle of the Devonian 

 period. 



The following species have been described : 



T. perforata, 



T. multistriata, 



T. costata, 



T. simplex, 



T. simplex var. from the Lower Helderberg group ; 



T. camura, from the Niagara group. 



