EARLY DEVONIC HISTORY OF NEW YORK AND EASTERN NORTH AMERICA 4 1 



contour, size and ribbing-. Here we have a pauciplicate shell, the dorsal 

 valve of which presents the characters which we have noticed as a feature 

 of Spirifer plicatus Weller of the Grande Greve limestones; few, 

 broad and blunt ribs. The shells are of the small size quite characteristic 

 of the genus with trihedral form and erect or but very slightly curved car- 

 dinal area, flat dorsal valve, median sinus and fold well developed, the 

 former having the width of the next two adjoining lateral plications. 

 There are four to five plications on each ventrolateral slope and three to 

 four on the dorsal, the ones nearest the hinge being always very faint. 

 These are in the main broad and smooth, and concentric growth lines 

 are usually crowded near the front margin. 

 Horizon. No. 9. 



Meristella princeps Hall 



Merista (Meristella) princeps Hall, Palaeontology of New York. 1S59. y.i^x, 

 pi. 44. fig- 1-5 



Occasionally in this fauna 

 Horizon. Nos. 1, 11. 



Nucleospira concentrica Hall 



Nucleospira concentrica Hall. Palaeontology of New York. 1S59. .3:223 

 pi. 28 B, fig. 15-19 



This species, common in the Helderberg fauna, is occasional at 

 Dalhousie. 



Horizon. No. 9. 



Trematospira perforata Hall var. atlantica Clarke 



Plate 7, figures 21-23 



Trematospira perforata Hall var. atlantica Clarke. N. Y. State Mus. Bui. 

 107. 1907. p. 262 



Species of Trematospira are almost exclusively of Helderbergian age 

 and the species described are pretty well defined on the basis of their sculp- 

 ture. In the form before us we have one more nearly allied in this respect 

 to T. perforata Hall than to any other, though it differs substantially 

 even from that. This shell has the following characters : The ventral 

 sinus is not bounded by the median primary pair of plications but by the 

 pair just outside the median, the latter in later growth making a pair 

 on the sloping walls of the sinus. Likewise the median rib on the 

 dorsal valve, while constituting the crest of the median fold is accompanied 

 by a pair of ribs of primary age which modify the slopes of the fold. At 

 the beak and continuing for one third the length of the shell without modi- 

 fication the number of plications on the ventral valve is 12, on the dorsal 



