Klem — Revision of the Palaeozoic Palae'echinoidea. 21 



ambulacra. Plates narrow and pierced near the opposite 

 extremity by two pores. Surface granulose. On the aboral 

 side the adambulacral plates bear the smallest tubercles, the 

 tubercles growing larger on the columns toward the center. 

 On the oral side the ambulacra alone bear tubercles. 



1. Lepidechinus imbricatus Hall. 



1861. Lepidechinus imbricatus. Hall, Desc. New Spec. 



(Jrin., p. 18. 

 1874. Lepidechinus imbricatus. Loven, Kongl. Svens. Ve- 



tens. Akad. Handl., Bd. 11, No. 7, p. 44. 

 1889. Lepidechinus imbricatus. Miller, N. Amer. Geol. Pal., 



p. 258. 

 1895. Lepidechinus imbricatus. Keyes, Proc. Iowa Acad. 



Sci., vol. 2, p. 192. 

 Eight columns in each interambulacrum, plates imbricating. 

 Ambulacra narrow, composed of short wide plates, deeply 

 interlocking at the joined edges and imbricating in the oppo- 

 site direction from those of the interambulacrum. The upper 

 adjacent angles of the interlocking edges are neatly rounded, 

 giving a curved outline to nearly half their width on the ex- 

 posed edge. Two small pores pierce each plate near its outer 

 extremity. Surface granulose. 



Geological formation and locality : Burlington Limestone, 

 Burlington, Iowa. 



2. Lepidechinus rarispinus Hall. 



1867. Lepidechinus rarispinus. Hall, 20th Rep. N. Y. State 



Cab. Nat. Hist., p. 295, pi. 9, fig. 10. 

 1870. Lepidechinus rarispinus. Hall, 20th Rep. N. Y. State 



Cab. Nat. Hist. (rev. ed.), p. 340, pi. 9, fig. 10. 

 1874. Lepidechinus rarispinus. Loven, Kongl. Svens. Ve- 



tens. Akad. Handl., Bd. 11, No. 7, p. 44. 

 1889. Lepidechinus rarispinus. Miller, N. Amer. Geol. 



Pal., p. 258. 

 1895. Lepidechinus rarispinus. Keyes, Proc. Iowa Acad. 



Sci., vol. 2, p. 192. 



