SUPPLEMENT. 



SIS 



Graptolithns marcidos. 



Fig. 1. A specimen more contracted than usual, with the serratures obtuse. 



Fig. 2. An individual presenting a more expanded form, with distinct den- 

 ticles at the lower extremity and a minute radicle below. 



Fig. 3. A young form where the serratures are not developed, or are flattened 

 in the line of their direction, and in which the minute fibres or ra- 

 dicles at the base are well preserved. The specific relations of these 

 forms have not been fully determined; and I am, at present, unable 

 to refer them to any other than this one. 



Geological position and locality. In the shales of the Hudson-river group : Near 

 Albany. 



Graptolithus anj^ustifolius ( n. s.). 



Stipes simple, linear, slender, biserrate : serratures well defined, the 

 denticles short ovate-acute, the extremities sometimes subobtuse ; base 

 marked by minute setiform radicles ; midrib projecting beyond the 

 serrated portion in a capilliform extension. Serratures arranged in the 

 proportion of about twenty-eight to thirty in the space of an inch; 

 This species has a narrow stipe with very distinct denticles, which are usually 

 closely arranged or apparently overlapping each other at the base, while sometimes 

 they are separated more distinctly and the indentation deeper. The form and pro- 

 portions of these denticles are dififerent from those of any species of GraptoHte in 

 the collections from these shales, and often more resembling the minute denticula- 

 tions on the fronds of fossil ferns than those of the graptolites. The denticles are 

 often subaltemate on the opposite sides of the stipe, and frequently variable in the 

 same individual. 



The accompanying figures illustrate the Usual characters of this species. 

 \ 



Fig. 1. A single stipe, twice the natural size. 



Fig. 2. A portion still fiirther enlarged. 



This species is associated in the same laminae of slate with G. 

 marcidus, G. whUfitldi, G. spinulosxts, and Heteograptus geini- 

 tzianus. 



1 2 



Geological position and locality. In the shales of the Hudson-river group : Near 

 Albany. 



