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On a New Genus of Fossil Cidaride, with a Synopsis of the 
Species included therein. By Tuomas Waiceut, M.D., F.R.S.E. 
Norwitustanpine the many new generic sections introduced 
into the classification of Echinoderms, by MM. Agassiz and 
Desor, and the important light thrown by these savans on our 
knowledge of the numerous species of this class contained in 
European collections, still the progress of discovery renders it 
imperative on palontologists to modify from time to time 
many of the opinions put forward by these authors in their 
‘ Catalogue raisonné.’ When the amount of real work done by 
them is taken into account, in a field which was then compara- 
tively unknown, the wonder is, not that mistakes or oversights 
should have been committed, but that so much good work 
under the circumstances should have been attained, which will 
bear the most severe criticism, and remain as it was left, a monu- 
ment of the genius and industry of the authors. 
In our memoirs on the Cidaride of the Oolites, we have 
figured and described three species, Goniopygus perforatus, Pe- 
dina Etheridgii and Pedina Bakeri; the true generic position of 
these forms seemed to us uncertain at the time our papers were 
passing through the press, as they exhibited characters which 
did not assimilate with either of the generic divisions of the 
‘Catalogue raisonné.’ Our materials did not then justify us in 
proposing a separate genus for their reception ; the discovery, 
however, of an interesting series of new congeneric forms has ~ 
now enabled us to rectify our determination, and propose the 
genus Hemipedina for the group, to which we have added a 
synopsis of the species included therein. 
Hemrrepina, Wright, 1855. 
This new genus is composed of small, neat, and highly orna- 
mented Urchins, much depressed on their upper surface, and 
with a flat or slightly concave base. The ambulacral areas are 
narrow and straight ; the pores in the poriferous zones are ar- 
ranged in single pairs; the interambulacral areas are in general 
more than double the width of the ambulacral, with two, four, 
or six rows of tubercles in general arranged abreast on the same 
tubercular plate. The tubercles are perforated, and set on mam- 
millary eminences with smooth uncrenulated summits; one row 
of tubercles in general only extends from the peristome to the 
disc; the other rows, when there are four and six rows in the 
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