C. E. Beeeher — Development of the B?*achiopoda. 353 



express other characters, but all included the same elements in 

 the two divisions. Professor Huxley's terms, the Articulata 

 and Inarticulata, have also come into current use, and are con- 

 venient to express the nature of the union of the valves. All 

 the names proposed for these divisions by Owen, Bronn, Hux- 

 ley, Gill, and King, are based upon (1) the intestinal canal 

 whether ending in an anus or in a blind sac, (2) the relative 

 proportions of the viscera and brachia to the shell cavity, and 

 (3) the character of the union of the valves. 



If, as Agassiz has said,* orders should be founded upon facts 

 of development or embryology, the ordinal division into groups 

 expressing the genesis of an important common character 

 should furnish a satisfactory classification. The Articulata and 

 Inarticulata do not appear to have a primary developmental 

 basis in nature. These names may be conveniently retained as 

 two divisions or sub-classes, but they fail to express the true 

 relationships of the various groups included in them. 



In 1883, Dr. Waagen (Palseontologia Indica) proposed a 

 classification comprising six suborders, founded partly on the 

 pedicle opening and on the form of the brachial supports. 

 Two of his groups, the Mesokaulia and Aphaneropegmata, are 

 nearly equivalent in extent to the Atremata and Protremata 

 now proposed. Daikaulia and Gasteropegmata of Waagen are 

 here included in the Neotremata, and the Telotremata comprise 

 the Kampylopegmata and Helicopegmata of the same author. 

 With the transfer of some genera in his suborders, they may 

 properly be recognized and serve further to differentiate the 

 class into comprehensive groups. 



After this preliminary discussion, the four groups proposed 

 can be defined and understood. The special details with full 

 illustration and demonstration of the development and affinities 

 in each group are left for future consideration. At present it 

 is aimed to give only the general results which have been 

 reached through the study of individual development (ontogeny) 

 among various species representing the families of nearly the 

 entire class. Of the sixteen families of Brachiopoda recognized 

 by (Ehlert in Fischer's "Manuel de Conchyliologie," fifteen 

 have thus been studied and determined. The genera marked 

 by an asterisk have been examined somewhat in detail. The 

 others have been investigated partly from adult specimens, and 

 from the published descriptions of the genera. 



* Methods of Study in Natural History, L. Agassiz. 8th ed., p. 76, 1873. 



