Ordouician Rocks. 57 



Only forms of fairly certain identity are given in this table; 

 more extended search will probably extend the range of some of the 

 species. The horizontal Didymograpti present difficulties which 

 minimise their suitability for use as zonal fossils, though it is f)rob- 

 able that detailed work with them will lead to instructive results. 

 Other forms such as T. serra and I'. quadrihracJiiafus appear to 

 range through all zones. T. nerra is vei'y common in some of 

 the beds of the Darriwil .series as constituted in this paper, 

 Goniograjitus is represented in the Middle Castlemaine beds by one 

 specimen of a new species and only one specimen of TJ. octohra- 

 chiatus has been found in Victoria Gully beds. Only tliree speci- 

 mens of Triaettograpfus, T. S. Hall, are known, and only two of 

 these were found in situ. The futility of using such species in an 

 account of zonal distribution is obvious, and, with a view to sim- 

 plicity, it has been thought better to give only the more useful spe- 

 cies. 



VIII. Classifications Compaped. 



It is apparent that this scheme of classification supplements the 

 older one. The following notes on the two classifications will serve 

 to show resemblances and differences : — 



1. Beds of the Darriwil series, as previously constituted, have 

 for the first time been recorded from the Castlemaine district. 



2. The meaning of the term Darriwil has been extended so that 

 in tlie Darriwil series are now included not only those beds referred 

 to the Darriwil by Dr. Hall, Init also jireviously unrecognised beds 

 between these and the Upper Castlemaine (Loga/io-cndiiceiix). zone. 

 I at first constituted these beds a new series under the name 

 " Yapeen," but I found later tliat apparently all these beds did 

 exist in the Darriwil district, and it seemed advisable to retain 

 that name for the series, thus giving it an extended meaning. This 

 alteration involved many alterations in the teixt, but was made too 

 late to enable the whole paper to be recast. 



3. The Castlemaine series remains as described by Dr. Hall. The 

 two zones of the Middle Castlemainian are not always distinguish- 

 able, and it was at first thought better to unite them. However, as 

 Dr. Halli after mature consideration separated them (they appear 

 as one zone in an earlier paper), it was decided to make no change. 

 The test for distinguishing them, " the comparative rareness of D. 

 caduceus "2 in the lower bed, is weak and not always applicable. 



1 Geol. Ciistlemaine, op. cit. 



2 Geol. Castlemaine, p. 70. 



