108 The Ottawa Naturalist [December 



Keyes, Missouri Geol. Surv., 4, 1894, p. 132, pi. IS, fig. 2, 

 Figure 2 presents the basal view of the theca, 

 copied from the Illinois report. 

 Jaekel, Zeitsch, d. deutsch. geol. Gesellsch.- 52, 1900, p. 676- 

 Comarocystites obconicus, Meek and Worthen. 



Meek and Worthen, Proc. Acad. Nat. Sci., Philadelphia, 

 1865, p. 144. Geol. Surv., Illinois, 3, 1868, p. 294- 

 pi. 1, figs. 2a, b. 



The total length of the theca of the specimen re- 

 presented by figure 2a probably did not exceed 20 

 millimeters. The appearance of the figure sug- 

 gests that the plates on the left side of the theca 

 were of enormous thickness, compared with their 

 width. This appearance is due, however, to the 

 growth of calcite in the interior of the theca, the 

 actual thickness of the plates thus represented 

 varying from about 1.5 millimeters, towards the 

 bottom- to almost 2 millimeters at the top of the 

 theca. Figure 2b represents the left side of an- 

 other specimen with the stereom protuberance, 

 formerly supporting the left pair of arms, at the 

 top. 

 Keyes, Missouri Geol. Surv, 1, 1894- p. 132, pi. 18. fig. 1. 

 Figure 1 is a republication of figure 2a of the 

 Illinois report. 

 26. The zoological position of Comarocystites. In 1896, 

 Haeckel separated from the remaining Cystidea those forms in which 

 no radial branching of the food^groove system, either trimerous or 

 pseudo-pentamerous, can be detected spreading over the upper surface 

 of the theca. These forms he distinguished as a co-ordinate group 

 under the name Amphoridea. Among the Amphoridea were placed 

 not only the asymmetric and bisymmetric forms but also those in 

 which the arms branch off radially from the top of the theca, without, 

 however, being attached dorsally, for at least a part of their length, to 

 the upper surface of the theca. To these Amphoridea with radially 

 arranged arms he applied the term Palaeocystida, and evidently re- 

 garded them as ancestral to the true Cystidea' especially to the 

 Glyptocystidae. Among these Palaeocystida, he placed the genus 

 Comarocystites. 



Bather (Echinoderma, 1900) retained the group Amphoridea, 

 but as one of the subdivision of the Cystidea, characterized by the 

 absence of radial symmetry in both food-grooves and thecal plates- 

 Corn arocystites, however- is referred by him to the Rhombifera. In 

 the Rhombifera, as defined by Bather, radial symmetry affects the 

 food-grooves, and the stereom and stroma are arranged in folds and 



