CONTRIBUTIONS TO PALEONTOLOGY. 341 



This species, in its generic features, is identical with L. imhricatus^ the 

 type of the genus from the Burhngton limestone ; and in its specific 

 characters it is very similar. 



The imbrication of the plates is a very marked feature in two speci- 

 mens of this species, and their condition is such as to leave no question 

 that the imbrication is from the ventral side, and not from the apex, 

 being the reverse of the relation described in the L. imbricatus ; and it is 

 possible that from the imperfect condition of the specimen described, I 

 may not have distinguished the relations of parts. In the species under 

 consideration, there is a central range of vertically imbricating plates 

 which cover the lateral margins of the adjacent ranges, so that the lateral 

 imbrication passes beneath them, instead of showing an alternation along 

 the central line or suture, as in the Burlington species. 



Formation and Localities. — In rocks referred to the age of the Chemung 

 sandstones: at Meadville, Pennsylvania (an impression in a specimen of 

 the rock associated with Crania leoni ? ) ; and in the ferruginous sand- 

 stones of Licking county, Ohio. The latter was received from Prof 

 Carter, formerly Professor of Natural History in the College at Gran- 

 ville, Ohio. 



The fossil from Meadville occurs in such position and relations that I 

 believe no one will question the geological horizon ; but the sandstones 

 of Licking county, Ohio, constitute the upper part of the Waverly sand- 

 stone series of that State, and have been referred, by many geologists, 

 to a higher position than the Chemung of New York.* 



GENUS EOCIDARIS, Desor. 



After a careful study of the " Echinus drydenensis " of Vanuxem, it was 

 found to possess certain characters which separate it from ARCHiEOCiDARis, 

 and also from Palechinus ; and the generic description below was written 

 before I had observed its similarity to the Genus Eocidaris, to which I 

 now propose to refer it. 



Body spheroidal, composed of five ambulacral and five interambulacral 

 fields. Ambulacra composed of a double series of plates, each per- 

 forated near its outer extremity by two small pores. Interambulacral 



* Since these pages have been in type, Dr. Newberry, Director of the Geological Survey of 

 Ohio, has announced the well marked distinctions of typical Chemung rooks with Spirifera 

 verneuili and Leiorhynchus mesacostalis, and the Waverly sandstones, which in that State consti- 

 tute a very distinct group. It now becomes very important to determine the soui'ce of the 

 Meadville specimen. 



