CHAP. 111. } THE CRUISES OF THE ‘PORCUPINE,’ 1038 
‘radioles,’ as the fossil spines of Cidarites are usually 
called, presenting a very marked character, had been 
found in various formations from the lower oolite 
upwards. ‘These spines are paddle-shaped, compressed, 
longitudinally grooved, flattened almost into plates, 
and strongly serrated on the edges. In the nummu- 
litie beds of Val-Dominico near Verona such spines 
were found associated with plates much resembling 
those of Cidaris, but with the unique peculiarity of a 
row of holes penetrating the test in the areolar space 
round the primary tubercle. This character our new 
Urchin does not possess, but the radioles have the 
flatness, the longitudinal strive, and the serrated edges 
of those of Porocidaris. 
I do not attach much importance to the perfora- 
tions in the plates. From Desor’s figures they are 
not round and defined in outline, but lengthened and 
somewhat irregular, and they radiate from the inser- 
tion of the spine. Our species has a set of depres- 
sions occupying the position of these perforated 
grooves which are undoubtedly for the insertion of 
the muscles moving the large long spines, and as the 
test is thin these grooves might readily penetrate the 
plate, or so nearly penetrate it as to be worn into 
holes by very little drifting or wear. 
Our recent species and the eocene form have 
another character in common; the areolar circles 
are not well defined, and the areolee tend to become 
confluent. 
Scattered plates only of this genus have been 
found fossil, and the ovarial plates were till now 
unknown. They present a very singular character, 
which is certainly of generic value. The ovarial 
