238 ROBERT TRACY JACKSON ON ECHINI. 



In the Permian, very few forms of Echini are known. In England and Germany Mioddaris 

 keyserlingi (Geinitz) occurs, and is important as the geologically second species known in the 

 Palaeozoic with two columns of plates in an interambulacral area. As far as at present defi- 

 nitely known, it and the new Mioddaris cannoni from the American Lower Carboniferous 

 are the geologically oldest members of the Cidaroida. In America, Archaeocidaris aculeala 

 Shumard and Swallow is reported as occurring in the Permian, and in India Archaeocidaris is 

 doubtfully represented by one species, A. forbesiana (Koninck), which is imperfectly known, 

 but is provisionally referred to this genus. Archaeocidaris selwyni occurs in the Permian of 

 Australia. In the American Permian is found Meekechinus ekgans gen. et sp. nov., which is a 

 very interesting type, as it has twenty columns of ambulacral plates in an area at the mid-zone, 

 being in this respect the most specialized of known Echini. It is the highest of the Lepides- 

 thidae and geologically the last of the series with more than two columns of ambulacral and 

 interambulacral plates in an area which is the essential feature of most Palaeozoic Echini. 



SYSTEMATIC DESCRIPTIONS. 

 Order BOTHRIOCIDAROIDA Jackson. 



Schmidt, 1874, p. 37. 



Bothriocidaridae Zittel, 1879, p. 480 

 Bothriocidaroida Jackson, 1896, p. 238. 



Regular Echini, with periproct enclosed by the oculo-genital ring. Two columns of plates 

 in each ambulacral area and one column of plates in each interambulacral area. 



Family BOTHRIOCIDARIDAE Klem. 



Bothriocidaridat (as an order) Zittel, 1879, p. 480; (as a family) Klem, 1904, p. 14. 

 With characters of the order. 



BOTHRIOCIDARIS Eichwald. 



Bothriocidaris Eichwald, 1860, p. 654. 

 Botriocidaris Neumayr, 1881, p. 4. 

 Botryocidarut Love'n, 1883, p. 57. 



Small spherical or elliptical Echini. Ambulacral areas relatively wide, about twice as 

 wide as the narrow interambulacra with their single columns of plates. Ambulacral plates 

 high, hexagonal, the pores of each pore-pair superposed in a depression in the center of each 

 plate. Interambulacral plates high, hexagonal, equaling the ambulacrals in height. Plates 



