LEPIDESTHES WORTHENI AND OTHER SPECIES. 209 



are three columns of plates. Four columns are not visible ventrally as 

 in the type. This differential character may be sufficient to base specific 

 difference on, but with present knowledge I should consider the speci- 

 men as Lepidesthes wortheni. 



Lepidesthes wortheni in the form of the plates and the configuration of 

 the fossil approaches nearest to Lepidesthes formosus, Miller (33), but differs 

 from it in having fewer columns of interambulacral plates. It differs 

 from other species of the genus in having fewer columns of both ambu- 

 lacral and interambulacral plates. 



NOTES ON OTHER SPECIES OF LEPIDESTHES. 



The genus Lepidesthes, Meek and Worthen, is an interesting member 

 of the Lepidesthidse on account of being represented by the largest num- 

 ber of species of any genus in the family and being therefore the best 

 known. Meek and Worthen (31) give a good figure of Lepidesthes coreyij 

 M. and W., which is from the Keokuk group of Crawfordsville, Indiana. 

 This species, which is the type of the genus, is characterized by 10 col- 

 umns of ambulacral plates which are sub-hexagonal and imbricating. 

 The plates of the interambulacrum are pentagonal in the adambulacral 

 columns, otherwise hexagonal. Meek and Worthen say of it that there 

 are, near the middle, 6 or 7 (rows) columns of plates, decreasing toward 

 the extremities, first to 5, then to 4, and so on to the ends, where each 

 seems to terminate in a single piece. The species Avas founded on a 

 single specimen in which the oral pole only existed ; therefore from their 

 statement we would gather the conclusion that the interambulacra orig- 

 inated ventrally in a single plate, like Pholidocidaris in this family (plate 

 9, figure 54) and Lepidechinus (plate 7, figure 42) of the Lepidocentridse, 

 and as the Echinus grew dorsally by addition of new rows of plates addi- 

 tional columns were progressively added until 6 or 7 were attained at the 

 ambitus. 



Studying Meek and Worthen's excellent figure of Lepidesthes coreyi,^ 

 we find that the interambulacrum at its ventral border, as far as shown, 

 has 4 columns of plates. A fifth column is introduced in the ninth row 

 from the bottom of the figure by a pentagonal plate, with a heptagonal 

 plate on its left. This column at its point of origin has 3 columns on the 

 left and one on the right. This is an irregular position for the fifth col- 

 umn, as odd-numbered columns characteristically originate in a median 

 position, with an equal number of columns on either side ; also the hep- 

 tagonal plate adjoining the terminal pentagon of odd columns ordinarily 

 occurs on the right. These variations, however, are just what are occa- 

 sionally met with in Melonites, and for comparison attention is directed 



*Geol. Survey of Illinois, vol. v, plate xvi, figure 2. 



