P K E F A C E . 



The following work consists of descriptions of new species of organic 

 remains from the Lower and Middle Silurian rocks, with re-descriptions, 

 and, in some instances, additional details and illustrations of a few that 

 were previously published either in the annual reports of the Survey or 

 in the scientific journals of the Province. It has been prepared from time 

 to time, according as the new forms were discovered, or as more perfect 

 specimens of those already known were procured. The only systematic 

 arrangement, therefore, that could be followed, was to group the descrip- 

 tions together in a series of articles. The first portion, consisting of 

 twenty-four pages, was issued in November, 1861, the second, pages 25 

 to 56, in January, 1862, the third, pages' 57 to 168, in June, 1862 

 the fourth, pages 169 to 344, in February, 1865, while the remainder, 

 completing the volume, will bear date herewith. The first twenty-four 

 pages, and also 57 to 72, have been reprinted with some alterations, the 

 substance of which is specified by Mr." BILLINGS in the appendix on 

 page 419. The figures were all drawn from nature by Mr. H. S. SMITH, 

 the artist of the Survey, and engraved on wood by Mr. J. H. WALKER 

 of this city. 



W. E. LOGAN. 



GEOLOGICAL SURVEY OFFICE, 



Montreal, October, 1865. 



