A. Olsson — New Genus of Palceechinoidea. 445 



end. Any variation in the ambulacral plates is of great 

 importance and must be considered of at least generic value. 

 Lepidechinoides differs also from Lepidechinus in its posses- 

 sion of fewer columns of interambulacrals and, more impor- 

 tantly, in having these plates more or less hexagonal in shape 

 and not scale-like as in the latter genns. In this latter char- 

 acter Lepidechinoides appears to represent a more primitive 

 form. Jackson in his Studies of Palseechinoidea* shows in 

 reference to Lepidechinus rarispinus Hall, that the rhombic 

 and hexagonal shape of the dorsal, or newly added interambu- 

 lacral plates, have phylogenetic significance, having characters 

 seen normally in less specialized genera and indicating deriva- 

 tion from forms which did not have imbricating plates. 

 Moreover those forms with scale-like imbricating plates are 

 specialized and not primitive types. 



From the Devonian of America there are at present three 

 genera and four species of Palseechinodea, representing two 

 families Lepidocidaridce Bather (Archceocidaridce McCoy) 

 and Lepidocentridm Loven. Yanuxem in his Report of the 

 3d Geological District, p. 184, mentions some doubtful remains 

 of echinoids from Dryden which he called Echinus drydenen- 

 sis. These specimens were later examined by Hall,f who 

 referred them to the genus Eocidaris Desor. They are 

 described as being from the shaly sandstones of the Chemung 

 group, 1,000 feet above the Tully limestone, representing 

 therefor the Eniield shales of the Portage formation. The 

 genus Eocidaris belongs in the family Lepidocidaridse and with 

 Xenocidaris clavigera Schultze of Europe are the only mem- 

 bers of the family found below the Sub-Carboniferous. The 

 family Lepidocentridm Loven is now represented in America 

 by the two genera Lepidechinus and Lepidechinoides herein 

 described. Of the genus Lepidechinus two species are known, 

 viz., L. rarispinus Hall from the Chemung of Pennsylvania, 

 and the Waverly group of Ohio and L. imbricatus Hall from 

 the Burlington limestone of Iowa. Lepidechinoides ithacensis 

 therefore represents the earliest known echinoid from America 

 although in Europe the genus Bothriocidaris Eichwald, of 

 which two species are known, is from the Ordovician. The 

 geological position of all the species in the family Lepidocen- 

 tridse is shown below : 



Lepidocentrus rhenanus Schultze 



" mulleri Beyr, middle Devonian of Muhlen- 



berg — near Geroldstein Eifel 

 " eifilianus Mtiller, Devonian of Nohn Eifel 



* Bull. Geol. Soc. of Am., vol. vii, p. 228, 1896. 



f 20th Annual Report of State Cab. Nat. Hist, of N. Y., 1868, p. 343. 



