DENDROID GRAPTOLITES OF HAMILTON, ONTARIO. 



25 



tion tlius being forcepslike. This mode of ending is quite characteristic of the 

 species. Apparently this spike-like forking of the branches may occasionally 

 take place in the wall of the poly pa ry below the summit, and the spikes then 

 seem to serve the same purpose as dissepiments, bracing the polypary. As the 

 fossil usually lies on the stone, the number of branches in 25 mm. of width is 

 exceedingly variable, generally from distortion. In places where the polypary 

 is evenly and smoothly laid out and the meshwork perfectly regular, however, 

 the number is about 22 (20-25) near the base and about 25-30 at the periphery. 

 The dissepiments are of medium thickness (about 0.15-0.4 mm.) and are either 

 perpendicular or highly inclined (say 45°) to the branches, and this combina- 

 tion in the same specimen forms a striking feature of this species, a feature 

 well shown in Spencer's figure (text fig. 29). Meslies very variable in shape, 

 corresponding to the irregularity in the branches and dissepiments. In one 

 specimen I find meshes from 1.5 to 6 mm. long, but the longest are in one or 

 two cases demonstrably subdivided, and prob- 

 ably 3 mm. is about the greatest length. From 

 obscure indications the thec:e seem to be set 

 about 50 in 25 nun. (Spencer gives the number 

 as 00.) 



One specimen (text fig. 20) in the Hall col- 

 lection shows the base fairly well preserved. 

 This measures about 12 by 8 mm. and shows a 

 unique structure. The margin is in places 

 sharply defined, and is either convex or con- 

 cave. The surface is uniformly dotted with 

 very numerous elliptic or circular pores, which 

 hardly reach 0.2 mm. in the greatest diameter, 

 and which have a well-defined rim-like margin. 

 They seem to have a somewhat regular arrange- 

 ment, in rows and are separated by interspaces 

 narrower than their own diameter. The tex- 

 ture of this " disk," like that of the network, is 

 carbonaceous. 



Horizon and locality. — Twenty-four specimens 

 from the Niagara chert and glaciated chert 

 bed.s, Hamilton, Ontario. 



In this count are included two specimens in the Spencei' collection, labeled 

 'Calyptouraptiis .sKbrctiforinift/' 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. trnelhim. 



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.(3 mm. (not 0.3 nun., as 

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

 mal 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 specimen of transverse 

 dissepiments and of dissepiments inclined at about 45° to the branches, with, 



Fig. 28. — Diction em a poly- 



MOEPHUM GUKLEY. OnE OF 



Spencer's ttpes of Calypto- 

 graptus subretiformis. 

 (After Spencer.) 



