446 ROBERT TRACY JACKSON ON ECHINI. 



idal muscles as usual in regular Echini. Below the pyramid E a distally forked plate occurs, 

 which is apparently a compass out of place (p. 182). 



The specimens of this species were collected recently by Professor J. W. Beede in the 

 Eskridge shales which are in the base of the Permian, at Grand Summit, Kansas. The three 

 specimens described, including the holotype and two paratypes, are in the collections of the 

 University of Kansas. 



The first species described in the systematic portion of this memoir is Bothriocidaris archaica 

 sp. nov. from the Ordovician, the oldest formation from which Echini are known, and that 

 species, as I have attempted to show, is most primitive in structure, having features in the adult 

 which are like the young of all succeeding Echini. On the other hand, Meekechinus elegayis, 

 which in the regular series is the last species considered, comes from the highest geological 

 formation, the Permian, in which the order Perischoechinoida is known. Structurally, as 

 regards the development of the ambulacrum and the possession of serrate teeth, it is the most 

 highly evolved of Palaeozoic species, and one of the most specialized of known Echini. As 

 regards the narrow interambulacra composed of only three columns of plates, it is also highly 

 specialized. It makes a fitting climax to the series of remarkable forms which are preserved to 

 us from these ancient geological formations. 



Incertae Sedis. 



In this section are considered all described Palaeozoic species of Echini that I cannot reason- 

 ably place in a definite genus, or intercalate in the systematic descriptions. 



Archaeocidaris konincki Desor. 

 Plate 15, figs. 13a-1.3d. 



Archaeocidaris konincki Desor, 1858, p. 155, Plate 21, figs. 7-10; Klein, 1904, p. 63. 

 Eocidaris konincki Lambert and Thieiy, 1910, p. 126. 



Known only from isolated interambulacral plates as figured. 

 Lower Carboniferous, Tournay, Belgium. 



Archaeocidaris ladina Stache. 

 Plate 15, figs. 15a-15d. 

 Archaeocidaris ladina Stache, 1877, explanation of Plate 5, figs. 11, 12; Lambert and Thiery, 1910, p. 125. 



Known only from small fragments of spines with rather large spinules. 

 Bellerophonkalke, Lower Carboniferous, St. Martin, South Tyrol. 



