WEAVER: INVERTEBRATE PALEONTOLOGY AND HISTORICAL GEOLOGY 705 



structure of these forms, with special attention to the position of the mouth in 

 relation to the ambulacral system. He concluded that the pores in the rhombs 

 of the Cystoidea were respiratory organs and the homologues of the tubular 

 apparatus which underlies the ambulacra of the Blastoidea. He pointed out that 

 Eocystites was the most primitive genus of the Cystoids, with an indefinite num- 

 ber of plates without any radial arrangement. He showed that the hydrospires 

 of the Blastoidea were connected in pairs and had direct communication with 

 the pinnulae. He thought that the mouth and anus combined represented the 

 opening in the disk of Paleozoic Crinoids and that the grooves which pass from 

 the center of the disk at the inner floor were conected with the ambulacral sys- 

 tem and communicated through the arm openings with the arm grooves but did 

 not enter the tegminal aperture. He considered that the food entered the body 

 through the arm openings and was carried underneath the tegmen to a common 

 oral center. Meek and AVorthen added to these morphological studies, with at- 

 tention to the ventral surface of the calyx, the plates, mouth, and anal openings. 



In North America little attention had been given to the Crinoids until 1858 

 but by 1897 over 1,400 species had been described. Until the publication of the 

 "Challenger" reports studies were confined largely to the abactinal side of the 

 calyx and no attempt was made to homologize the plates of the tegmen of the 

 different groups. The excellently preserved and abundant faunas of the late 

 Paleozoic in the Mississippi Valley drew the attention of Wachsmuth and 

 Springer, who, during the last quarter of the nineteenth and first quarter of 

 the twentieth centuries, contributed many important papers and monographs 

 on the Pelmatazoans. Among these was a three-volume work published in 1897 

 by the Museum of Comparative Zoology on The North American Crinoidea Ca- 

 merata. Special consideration was given to morphological and phylogenetic 

 characters, with an accompanying classification which is widely accepted at the 

 present time. They point out "that the Crinoids were most intimately connected 

 from the Silurian down to the present and only the Camerata, a highly special- 

 ized type, became extinct at the close of the Paleozoic." All American species 

 of the Camerata known at that time were described in this monograph. They 

 noted that the Crinoids, Blastoids, and Cystoids differ from other Echinoderms 

 in being at one stage of life provided with a stem for attachment to other objects, 

 thus living on their abactinal side in contrast to the other groups. Other im- 

 portant later contributions have been made by Jaekel on the phylogeny of the 

 Pelmatazoa, by the revised textbooks of von Zittel, and by R. S. Bassler on 

 the Edrioasteroidea. 



Although many genera and species of Echinoids were described during the 

 first half of the nineteenth century, the scientific approach to the investigation 

 of the morphology and phylogeny began with the contributions made by Agas- 

 siz and Desor in 1840. These were followed during the next seventy-five years 

 by the publications of Forbes, d'Orbigny, Wright, and Cotteau in Europe and 

 by Hall, W. B. Clark, Twitchell, and Jackson in North America. The compre- 

 hensive monograph by Jackson in 1912 on the phylogeny of the Echini presents 

 the information and interpretations made by numerous authors both in Europe 

 and America, together with his own study of the morphology, development, and 

 comparative anatomy of this class founded on the young and adult of fossil and 

 living forms. His contribution includes a revision of the Paleozoic Echini and 



