22 Trans. Acad. Sci. of St. Louis. 



1896. Lepidechinus rarispinus. Jackson, Bull. Geol. Soc. 

 Amer., vol. 7, p. 226, pi. 7, figs. 1, 2. 



Test spherical or depressed spheroidal. Interambulacrum 

 composed of from seven to nine columns of plates, which 

 imbricate from below upward and from the middle outward. 

 Large central tubercle on each plate. In this species there is 

 a central range of vertically imbricating plates which cover 

 the lateral margins of the adjoining columns, making the lat- 

 eral imbrication pass beneath, instead of showing an alter- 

 nation along the middle line. Ambulacra narrow, composed 

 of two rows of small low plates, each pierced by two pores 

 near the distal extremity. 



Geological formation and locality: Chemung, Meadville, 

 Pa.; Waverly, Licking Co., Ohio. 



II. Lepidesthidae Jackson 1896.* 



Spherical or subspheroidal test. Six or more columns in 

 each ambulacrum and generally ten in each interambulacrum. 

 Plates imbricate. Pores in the center of each ambulacral 

 plate. 



a. Pholidocidaris Meek and Worthen 1869. t 



Ambulacra quite broad composed of six columns of small 

 irregular oval or rhombic plates, imbricating aborally and 

 provided each with a tubercle and two pores in a deep furrow. 

 Interambulacrum consists of five or more columns of thin, 

 rounded, arched, granulated, irregular plates, imbricating 

 aborally and outward. Adambulacral plates three or four 

 times as large as the others. On the lower (?) side the in- 

 terambulacral plates have a central, perforated primary 

 tubercle. Spines large and striated. 



1. Pholidocidaris IRREGULARIS Meek and Worthen. 



1869. Lepidocentrus irregularis. Meek and Worthen, Proc. 

 Acad. Nat. Sci. Phil., p. 78. 



* Bull. Geol. Soc. Amer., vol. 7, p. 241. 

 t Proc. Acad. Nat. Sci. Phil., 1869, p. 78. 



