CONTRIBUTIONS TO PALAEONTOLOGY. 89 



marked by an interrupted row of nodes, and sometimes by two unequal rows 

 of nodes : in the perfect crust, these nodes may have been produced into 

 spines. The border is narrowly thickened, sinuate on the margin, and, at the 

 extremities of the ribs, is produced into long slender curving spines. Margin 

 of the caudal extremity concave. 



From the dimensions of the pygidium, this species has been by far the 

 largest trilobite in the higher rocks of our system. 



Geological formation and locality. In the limestone of the Upper Hel- 

 derberg group : in the Helderberg mountains ; Schoharie ; and in Genesee 

 county, N.Y. 



DALMANIA HELENA (n.s.) 



Pygidium large, subtriangular, depressed -convex, the axis little 

 elevated, the posterior extremity bending upwards, and the 

 border concave or emarginate : the axis tapers gradually; its 

 width at the anterior end is equal to half the width of the la- 

 teral lobes, marked by twenty-one or twenty-two annulations 

 (some of the posterior ones being perceptible in the cast). Lateral 

 lobes marked by eighteen or nineteen ribs, which terminate in a 

 narrow, thickened, somewhat undulating border. 

 Surface granuloses the ribs marked by two rows of nodes or short 

 spines. 



The description of this species was prepared for the press before I had 

 had an opportunity of seeing anything more than fragments of the D. myt' 

 Tnecophorus, and the similarity between the two is very marked ; but unless 

 that one is subject to extreme variations, this is a distinct species. The 

 length and width of the pygidium are about as two to three, while in D. 

 myrmecophorus the width is twice the length : the width of the axis in that 

 species is a little more than one-third the width of the lateral lobe ; and in 

 this one, the axis measures half the width of the lateral lobe. 



Geological formation arid locality. In limestone of the Upper Helder- 

 berg group : near Columbus (Ohio), and in New-York. 



DALMANIA CALYPSO ( n. s.) '^ 



Pygidium paraboloid, very convex, the axis sharply angular : an- 

 nulations about fifteen or sixteen (the posterior ones visible in 

 the cast), surmounted by a row of short spines. Lateral lobes 

 marked by twelve or thirteen gently curving narrow ribs, which 

 terminate in a well defined border of moderate width. Length 

 of specimen one inch : width across the anterior margin, nearly 

 one inch and three-eighths. 

 1861.] . 12 , [Senate No. 116.] 



