80 NEW YORK STATE MUSEUM 



the length of the shell, there is no thickening at the beak and the hinge 

 plate is so slender that we have 'been unable to make it out. All these 

 details are in notable contrast to R. atlantica, R. stewarti and 

 the Coblentzian species referred to. 



They are in closer correspondence to the Helderberg species R. 

 aequiradiat.a Hall and indicate, irrespective of their considerable size, an 

 entirely primitive condition of development. The markings of the surface 

 consist of simple rounded or slightly flattened plications seldom with concen- 

 tric growth lines or other interruptions. There are about 50 of these simple 

 plications on each valve, the number varying very little with size and age. 



Localities. Miser)- stream, first dam in town of Sandwich ; Brassua 

 lake, opposite Moose river, Me. 



Rensselaeria diania Clarke 



Plate 18, figures 4-6 



Rensselaeria diania Clarke. N. V. State Mus. Bui. 107. 1907. p. 242 



This species retains the contour and simple structure of R . c a 1 1 i d a 

 but differs wholly in its exterior which carries 20 to 30 very coarse and 

 broad, sometimes quite sharply keeled plications which meet in sharp inter- 

 locking angles at the edge. Its similarity to R. crassicosta Koch of 

 the Siegen greywacke is undeniable, and we have introduced some figures 

 of that shell for purposes of comparison. 



Locality. Misery stream, first dam in town of Sandwich, Me. 



Rensselaeria cf. crassicosta Koch 



Plate 17, figures 7-q 



See Koch. Neues Jahrb. fiir Mineral. 1801. 11237, and other German authors 

 Rensselaeria cf. crassicosta Koch N. Y. State Mus. Bill. 107. 1907. p. 243 



There are a few shells of small size in a quartzite at the above cited 

 locality which are coarse ribbed and hardly to be distinguished from speci- 

 mens of R. crassicosta which 1 have received from Professor Kayser. 

 The dorsal valves show a long and much thickened septum with a divided 

 hinge plate. 



R. crassicosta is from the Taunus quartzite and Siegen beds of 

 the Coblentzian. 



Locality. Misery stream, first dam in town of Sandwich, Me. 



