214 R. T. JACKSON — STUDIES OF PAL.EECHINOIDEA. 



fragmentaiy interambulacra are almost completely covered by the large, 

 thickly associated spines. One of these specimens (catalogue number 

 3035) has the buccal pyramids in place, which structures have not been 

 described in the species. 



A second species, Archmocidaris drydenensis, Vanuxem, was described 

 first as Eocidaris, then as Archasocidaris b}^ Shumard, and later as Eocidaris 

 by Hall (17). Dr Duncan (9) considers that Eocidaris is a synonym of 

 Cidaris, having no distinctive characters ; therefore the species in question 

 cannot be included in that genus. The type, which is in the New York 

 State Museum at Albany, I have not seen, but a cast of the t3^})e in the 

 American Museum in New York would seem to be referable to Archasoci- 

 daris, where Ke3'^es (24) includes it in his recent " Synopsis of Paleozoic 

 Echinoids." This species has 7 columns of interambulacral i)lates, thus 

 exceeding in this feature any other known species of the genus. The 

 species has never been figured.* 



Another species, Archasocidaris loortheni, Hall (15), was described from 

 perhaps the best material known in au}^ species of the genus. This ma- 

 terial was in the Hall collection and is now in the American Museum of 

 Natural Histor}'- in New York. The specimens, which are from the Saint 

 Louis group, Subcarboniferous, of Saint Louis, Missouri, consist of a large 

 slab containing several more or less complete individuals ; also several 

 smaller specimens consisting of more or less complete tests, dissociated 

 plates, jaws and spines. All the most complete specimens have 4 columns 

 of ])lates in each interambulacral area. 



The best specimen, which is free from the matrix, was figured by Hall.f 

 This specimen is in a very fine condition of preservation. Hall's original 

 figure, drawn by Meek, shows the general features, and additional fea- 

 tures are shown in my plate 8, figure 43. This figure is oriented, as in 

 Hall's original figure, for easy comparison when such is desired. Inter- 

 ambulacrum A at the ventral border of the corona has a row of 4 plates, 

 c, d, e,/.§ Plate c of column 1 is nearly entire, but its ventral border has 

 been partiall}^ resorbed by the encroachment of the peristome on the 



* It is an important matter of scientific information to know where the types of species and fig- 

 ured specimens are located; therefore in Ihis paper I have given this information in regard to 

 the species considered wlien known. The following species are not otherwise mentioned, but it 

 is worth recording that the types are In the Illinois State Museum at Springfield, Illinois (see foot- 

 note, page 207). Archceocidaris cdgarensis, W. and M.,iUinoisensis, W. and M.,spiniclavaia, W. and M., 

 and Archceocidaris, sp. undetermined, W. and M., jaws. (Geological Survey, vol. iii,vii, plate xxx, 

 figure 16.1 The types of the following species are in the Worthen collection at the University of 

 Illinois, Urbana, Illinois (see foot-note, page 136): Archceocidaris keokuk, Hall, mucronata, M. and W., 

 shumardana, Hall. The type oi Archceocidaris legrandensis, Miller and Gurley, is in the private col- 

 lection of Wm. F. E. Gurley, at Springfield, Illinois. 



t Report of the Geological Survey of Iowa, vol. i, plate 26, figures 4a and 46. Figure 4a has been 

 frequently reproduced in text-books, as Zittel's and Nicholson's Manuals of Paleontology. 



§ The ventral plates of this and other areas are only partially shown in the original figure. 



