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PROFESSOR WYVILLE THOMSON ON THE ECHINOIDEA OF THE 
small pedicellarias in Pliormosoma. The valves are somewhat thicker and stronger and 
wider at the distal end in proportion to the width of the base, therefore widening out 
more. The head of the pedicellaria has thus more the form of an inverted cone. 
The tube feet on the oral surface of the test are cylindrical, expanding distally into 
a sucker, which is supported by a fenestrated calcareous disk in four, five, or six pieces, 
with the edge produced into an irregular spiny border. Irregular cribriform plates 
(Plate LXIV. fig. 3) are imbedded in the walls of the tubes on both surfaces of the 
body. The tube feet on the apical surface are conical and pointed, with neither sucking- 
disk nor terminal pit. 
The ovarial plates are complete and triangular in form ; the aperture is very large, 
and filled in with a membrane of a dark purplish colour. As has been already said, 
the interambulacral plates, while overlapping towards the apical pole, bend strongly 
near the middle line of the area towards the mouth. The triangular space thus left 
between the first.pair of plates of the series is occupied in four of the areas by the large 
ovarial plates, and in the fifth by the still larger ovarial plate, which is partly modified 
into the madreporiform tubercle. The membrane of the periproct is thickly set with 
discoid plates, becoming gradually smaller towards the circumference of the anus, and 
studded with small spines and small pedicellarise. The ocular plates are club-shaped, 
and touch the outer angles of the ovarial plates on either side. A strong calcareous 
ridge runs across each ambulacral area at the border of the peristomial opening of the 
test, soldering its plates together, and rising up at the edge of the ambulacral area into 
a rod which forms one half of the auricle, which arches over the ambulacral space by 
uniting by a small anchylosed suture with the corresponding rod on the other side. 
The peristomial membrane is covered by twenty rows of densely imbricated scales in 
ten double rows, corresponding with the ambulacral and interambulacral areas of the 
test. The plates of the peristome are all imbricated towards the mouth. The scales 
of the five double rows, corresponding with the ambulacra, are perforated towards their 
outer angles with double pores, which carry the tube feet up to the edge of the oral 
opening. The peristomial scales are studded with small tubercles bearing small spines 
and many pedicellariae. The edge of the peristomial aperture is entire, as in Cidoris , 
without branchial notches. 
The dentary pyramid is broad and low. The pairs of jaws are broadly triangular ; 
the epiphyses are small, and show no tendency to form an arch. The rotulee are wide 
and strong. The teeth have much the character of those of Diadema , being narrow and 
coming to a long point, and being simply grooved without the characteristic inner ridge 
of the Echinidse. 
The colour of the perisom is a brilliant deep rose inclining to claret-colour ; twenty 
bands of deeper shade run in pairs, alternately closer and more remote from one another, 
along the ambulacral and interambulacral spaces. The ends of the spines are pale pink, 
and the tube feet are nearly white. 
The specimen of Calveria hystrix from which the above description was taken, the 
