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PEOEESSOE WYVILLE THOMSON ON THE ECHINOIDEA OE THE 
O. F. M tiller, and several others) are members of the same fauna described from the 
seas of Scandinavia and Greenland, but not hitherto known as British. A third section, 
consisting of a number of undescribed Echinoideans, Asterideans, and Ophiurideans, 
may probably also belong to this fauna ; while a fourth group, likewise undescribed, 
and including such forms as Porocidaris, Phormosoma, Calveria , Pourtalesia, Neolampas, 
Zoroaster , Ophiomusium , Pentacrinus, Phizocrinus, and Bathycrinus , would rather appear 
to be referable to a special deep-sea fauna of which we as yet know only a few examples, 
and with whose conditions and extension we are unacquainted. This abyssal fauna is 
of great interest, inasmuch as nearly all the hitherto discovered forms referred to it 
show close relations to family types of Cretaceous or Tertiary age, and hitherto supposed 
to have become extinct. 
Twenty-seven species of Echinoidea were procured during the cruises of 1868, 1869, 
and 1870, off the coasts of Britain and Portugal, at depths varying from 100 to 2435 
fathoms. 
Class ECHINOIDEA. 
Order I. Desmosticha (E. Hackel). 
Family 1. Cidarid^e. 
Test globular. The plates of the test are thick and abut against one another in 
vertical surfaces, showing no tendency to overlap. The ambulacral areas are very narrow, 
usually slightly undulating ; they are composed of numerous plates which bear miliary 
granules only, and these usually in not more than six rows. The poriferous zones are 
narrow : the pores of a pair are usually contiguous ; sometimes they are a little remote 
from one another, and are united by a shallow groove. The interambulacral areas are 
very wide, from three to five times the width of the ambulacral ; they consist of two 
rows of large plates, each plate bearing one large scrobicular areola more or less depressed 
and encircled by a raised rim : in the centre of the areola a prominent boss, sometimes 
crenulate and sometimes smooth, bears a large smooth perforated mamelon. 
The oral and apical openings are very large. The peristome is round or slightly 
pentagonal without notches. The peristomial membrane is closely mailed with twenty 
rows of thick calcareous scales, five double rows ambulacral and five interambulacral, 
imbricating towards the mouth. The ambulacral scales are perforated for the passage 
of tube feet, which are continued from the pore-areas of the corona in double series up to 
the edge of the mouth. The free edges of the scales bear granules, to which are attached 
small flattened spines and pedicellarise. 
The apical disk is large and rounded, and consists of five large genital plates (one of 
them modified to include the madreporic tubercle) and five ocular plates. The anus is 
central, directly opposite the mouth ; and the membrane of the periproct is clothed with 
a varying number of irregularly formed thick plates and calcareous granules, which form 
a continuous pavement round the anal aperture. 
The dental pyramid is strong and well developed. The outer angles of the two divi- 
