30 THE PROCEEDINGS OF THE LINNEAN SOCIETY 



beds, I believe to be essentially upper Silurian, and one portion 

 at least to represent the equivalent to the lower part of the upper 

 Silurian of other countries. 



No fish bones have yet been discovered, so that at present the 

 Yass Period satisfies the requirements of the Silurian formula : 

 a Fauna represented by invertebrates, of which the Articulata 

 are chiefly Trilobites ; and a Flora by Fucoids. To the Trilobites, 

 however, we must look for the most decisive testimony. The 

 fact of Calymene ranging all through the fossiliferous portion 

 of the Hume beds, and Glieirurus and SjpJierexoclius ranging 

 nearly through — these being exclusively Silurian genera, is 

 almost sufficient evidence in itself from which to class these beds 

 as not newer than the upper Silurian ; while the absence of any 

 Trilobites of exclusively lower Silurian genera afibrds a 

 presumption that they are not older, which presumption is 

 strengthened by the presence of 0. reticularis and Pentameri. 

 The presence of the large Triiobite closely allied, if not identical 

 with Phacops caudatus and having no resemblance to the Devonian 

 species of Phacops — and of the Homalonotus which is not of the 

 characteristic Devonian type, all add force to the evidence afibrded 

 by the frequent occurrence of the other Trilobites. The only part of 

 a Triiobite with a Devonian aspect I have found in the Yass beds 

 is the Globular Glabella. The variety of Orthidce, of Silurian 

 species, as OrtJiis elegantula, helps to stamp these beds Silurian. 

 While the abundance of Pentameri, especially the presence of 

 Pentamerus ohlongus, support the inference that part of these 

 beds may rightly be considered to represent the lower part of the 

 upper Silurian. The presence of a Maclurea must not be forgotten. 



Pentamerus ohlongus is especially relied upon by Sir R/oderick 

 Murchison as determining the strata in which it occurs, in 

 Europe and America, to be the equivalent of the Llandovery of 

 the British Siluria. The Cheirurus found in these beds is 

 Cheirurus insignis, a Llandovery species. (Recherches, sur les 

 fossiles, Paleozoiques de la Nouvelle Galle De Sud, par L. C. 

 De Koninck). f 



t The following is a list of fossils, which, in Professor Koninck's work 

 already quoted, are classed as Devonian, and said to be found in the 



