Report of the State Geologist. 163 



" Yolume lY, Part II." Those lithographed since 1888 are 

 designated as Yolume YIII, and while the illustrations of the 

 first named plates are not alwa^^s arranged as would have been 

 done with later knowledge and more abundant material, it is 

 hoped that the intercalation of the new plates may not seriously 

 interfere with the proper connection and continuity of the work, 

 or with the facility of reference so important to the student. 

 Although the final numbering is XX, the actual number of plates 

 in the volume is forty-two. 



The printing of this volume had been completed to the end of 

 the Inarticulata, page 183, in March, 1890, when further progress 

 was suspended, from causes over which the author had no con- 

 trol. The printing was resumed in the autumn of 1890, and the 

 book was in type to page 304 in February, 1891, when its progress 

 was again suspended to be resumed only in April, 1892. This 

 delay in publication, which has not in any way been due to the 

 author, requires an apology to the scientific public ; and those 

 authors who may have published papers relating to the Brachio- 

 poda, during 1890 or 1 -^91 which could not be cited in this volume, 

 will here find the explanation. 



At the time this work was commenced the earliest known 

 articulate Brachiopod had been described under the name of 

 Orthis, and without having the knowledge or means to verify or 

 disprove the character of this fossil, the genus Orthis was 

 adopted for the basis of discussion. Had these older forms been 

 better known, the order of the work might have been somewhat 

 modified. The other associated and succeeding genera have been 

 taken up and treated after the same idea as in Orthis ; limiting 

 the discussion to those which seem to be a natural result of the 

 modification of certain essential organic features characterizing 

 the earliest forms of the orthoid type. 



Following this order and method we pass through all the 

 Orthid.e, the strophemenoid and streptorhynchoid forms in their 

 varied aspect and modification, and through the leptaenoid forms 

 to Chonetes and the Productid^ proper, with which the series 

 seems naturally to end. 



All the spire-bearing forms, all the Rhynchonellidj^ and 

 Pentamerid.e as well as the terebratuloid forms have been left 

 out of consideration in the present volume, believing that a more 



