o:^ 



PERMIAN FOSSILS. 



Cyathocrinus ramosus occurs rarely in the Shell-limestone at Tunstall Hill and 

 Silksworth ; abundantly in the corresponding rock at Humbleton Hill ; and rather 

 uncommonly in the Breccia at Tynemouth. Geinitz records its occurrence in the 

 Lower Zechstein of Corbusen ; and in the Zechstein-Dolomite of Asbach, Schmal- 

 kalden, Posneck, and Kamsdorf. According to Schlotheim, it is found at Gliicksbrunn 

 and Liebenstein. 



Order Echinideji;, Cuvier. 



This order, of which the common Sea-urchin {Echinus esculentus) of the English 

 coasts is a good representative, consists of a large number of genera, both living and 

 extinct ; but the following one is the only form known to be Permian. 



Genus Arcliceocidaris, M'Coy. 



Diagnosis. — " Interambulacra composed of three or more rows of plates, those on 

 each side, next the ambulacra, pentagonal ; those of the immediate rows hexagonal, as 

 in PalcBcJiinus ; each plate having in the centre one large perforated tubercle, surrounded 

 by an elevated ring, as in Cidaris, each of which tubercles bears a large, mobile, 

 generally muricated spine."^ (M'Coy.) 



" It is a singular circumstance that, except Professor Agassiz, every author, who 

 has treated of the Echinodermata of the Mountain-limestone, should have referred the 

 hexagonal plates with the above characters to the genus Cidaris, when a glance at the 

 re cent or Oolitic Cidarites would be sufficient to show that in their entire framework 

 there is not one hexagonal plate, both the ambulacra and interambulacra being composed 

 each of two rows of pentagonal plates only, while in \he present genus, as m Palachinus, 

 their interambulacra must have been composed of more than two rows, as is obvious 

 from their hexagonal form ; the large, perforated tubercle, however, is precisely in 

 accordance with that of the true Cidaris, as is also the mode of attachment and 



general character of the large spines with which both genera are armed I 



had long ago distinguished this genus in ray MSS. under the name of Archaocidaris, 

 subsequently Professor Agassiz announced his intention of forming the genus EcJiinocrinus 

 for the Cidaris Nerii, &c."'^ 



Though Agassiz's name is adopted by Professor M'Coy, yet later writers, from the 

 circumstances above related, have been led to give the preference to the name 

 Archaocidaris. M. Agassiz, with his colleague M. Desor, has lately changed the name 

 into FalcBocidaris. 



^ Carboniferous Limestone Fossils of Ireland, p. 1 73. 

 2 Idem. 



