GRAPTOLITES OF NEW YORK, PART 2 l6l 



length. From obscure indications the thecae seem to be set about 50 in 25 

 mm (Spencer gives the number as 60). 



One specimen [pi. 3, fig. 6] in the Hall collection shows the base fairly 

 well preserved. This measures about 12 mm by 8 mm and shows a unique 

 structure. The margin is in places sharply defined, and is either convex or 

 concave. The surface is uniformly dotted with very numerous elliptic 

 or circular pores, which hardly reach 0.2 mm in greatest diameter, and 

 which have a well defined rimlike margin. They seem to have a somewhat 

 regular arrangement in rows and are separated by interspaces narrower than 

 their own diameter. The texture of this "disk" like that of the network, 

 is carbonaceous. 



Horizon and locality. Twenty-four specimens from the Niagara chert 

 and glaciated chert beds, Hamilton, Ontario. 



In this count are included two specimens in the Spencer collection, 

 labeled " C al y p t ogra p t u s subretiformis." While these two 

 specimens are very poor, still without question they belong here and not 

 with C . subretiformis. On the other hand, it is quite evident to me 

 that these two specimens are of the species which furnished the basis for 

 Spencer's figure 2, which differs considerably from his figure 1, and his 

 figure 2 should therefore, I believe, be added to the synonymy of D . 

 tenelTum. 



This species is exceedingly variable in appearance. It is sometimes 

 spread out circularly, sometimes flattened flabelliformly from the side. Its 

 most characteristic features are the average thickness of 0.6 mm (not 0.3 mm, 

 as Spencer's text states), their number of 20-25 in 25 mm of width in the 

 proximal, and of 25-30 in the distal portion of the polypary. But in this 

 species more than in others, it is possible to get almost any number, unless 

 the place for counting be carefully chosen, where the meshes are regularly 

 laid down and not distorted. Further, the combination in the same speci- 

 men of transverse dissepiments and of dissepiments inclined at about 45 to 

 the branches, with, in other places, modes of connection (coalescence of 

 approximated lateral margins, curving together and entire fusion of adjacent 

 branches) usual in Desmograptus, thus producing a great variety of mesh 

 form, constitutes a striking feature in the present species. 



Remarks. In the Rochester shale at Middleport this is one of the 

 most common graptolites. It attains there considerable size, patches 

 indicating a diameter of 22+ cm of the rhabdosome when flattened to a 

 circle, being found. Smaller fragments of the same form have also been 

 noticed at the base of the Rochester shale, directly above the Clinton shale 

 at Palmer's glen, near Rochester and the collection of the National Museum 



