23o NEW YORK STATE MUSEUM 



and Arkansas [Gurley]. Lapworth considered it the most typical grap- 

 tolite of this zone in Canada (zone of Coenograptus gracilis), and inferred 

 from his material that it did not enter the following zone ("zone with- 

 out Coenog. gracilis"). Though Ami later found it in the latter, it is 

 evidently very rare there and thus remains a good index fossil of the 

 Normanskill shale or Dicellograptus zone. In the Monograph of British 

 Graptolitcs it is designated as " one of the commonest fossils wherever the 

 graptolitic facies of the Upper Llandeilo rocks is developed" and stated to 

 occur "in abundance" throughout S. Scotland, "where the central members 

 of the Glenkiln beds occur." It is also cited from many localities in Wales, 

 Shropshire and Ireland and gives its name to a zone in Great Britain 

 that corresponds to our Normanskill shale. It likewise characterizes the 

 corresponding zone in Sweden and is known from Australia. 



Rcmarhcs. The original mode of growth of this graceful form is difn- 



o o o 



cult to decipher from the flattened shale material. The conception of an 

 S-shaped main stem whose one half is ascending and the other descending 

 produced by the compressed material, is not supported by the appearance 

 of the thecae. Elles and Wood have commented on the fact that the 

 thecae of the main stipes appear sometimes on the inner and sometimes on 

 the outer side of the curve and explained this fact by a slight torsion of the 

 main stem produced at the time of its coming to rest by the presence of the 

 secondary branches. 



From a survey of our material we would co.nclude that originally both 

 main stipes were ascending, forming a rather wide lyre-shaped figure but at 

 the same time did not lie in the same plane but would have formed, it con- 

 tinued sufficiently, a very slender double spiral. The observations support- 

 ing this view are the following: The variety surcularis shows the 

 extreme upward growth of the branches in this group and at the same time 

 always exhibits a crossing of the distal parts, that is indicative of their 

 growth in different planes. The longitudinal view of the sicula is hardly 

 ever shown in N . gracilis and the two primary and some of the follow- 

 ing thecae as a rule are seen from the dorsal side with the transverse section 



