202 DEVONIAN FAUNA. 



the test in its original shape could hardly have been less than three inches in 

 diameter, and possibly was considerably larger. 



Affinities. — Lepidcsthes Corey i, Meek and Worthen, 1 differs in having much 

 smaller and more numerous (eighteen to twenty-five) warts, which are all equal 

 in size, both on the interambulacral and ambulacral plates. Its test also appears 

 to have been much smaller. 



II. Family — Arch^eocidaiud^;, M'Goy, 1855. 

 1. Genus — Peotocidaris, gen. nov. 



Interambulacral plates with a small central perforated tubercle, consisting of a 

 minute mamelon on a base without a distinct areola or bounding ring round the 

 base, and with five or six minute subsidiary tubercles. Spines acicular, finely 

 striated. 



The central perforated tubercles show that the species described below may 

 be regarded as belonging to the family Archseocidaridse, but the absence of a 

 "ring or slight projection round their base" excludes it from the genus 

 Archseocidaris, in which genus, moreover, the spines are (with very rare excep- 

 tions) covered with thorny points. 



Neither does it appear referable to Eocidaris, Desor, 2 though it agrees with it 

 in the absence of the bounding ring or slight projection. In that genus as 

 described by Hall, 3 and in E. Drydenensis, Vanuxem, sp., 4 it is stated that there is 

 only one spine to each plate, whereas our species would seem to have had several 

 subsidiary spines. Desor, moreover, in his original description, states the spines 

 to be spinuliferous, whereas ours are simply striated. 



In Lepidoc'uhnis? which appears to be a genus founded by Meek and Worthen 

 for their Eocidaris ? squamosus, 6 the central tubercles appear very much larger, 

 bordered by a groove, though without a bounding rim, and surrounded on the 

 margins of the plate by crowded granules ; its spines, however, are similar in 

 shape to ours. 



There seems, therefore, only to remain the genus Lepidechiniis, 7 with which 



1 1868, Meek and Worthen, ' Geol. Surv. Illinois,' vol. iii, p. 525, woodcut a. 



2 1858, Desor, ' Synopsis des Bchinides Fossiles,' p. 155. 



:5 1867, Hall, 'Twentieth Kept. Eegent's Univ. N. T.,' p. 297. 



4 Ibid., p. 298. 



5 1873, Meek and "Worthen, ' Geol. Surv. Illinois,' vol. v, explan. of pi. ix. 

 G Ibid., p. 478, pi. ix, figs. 15 a— y. 



7 1861, Hall, ' Desc. N. Sp. Crinoidea,* Preliminary Notice, p. 18. 



