HAP. IIL] THE CRUISES OF THE 'PORCUPINE.' 103 



radicles/ as the fossil spines of Cidarites are usually 

 3alled, presenting a very marked character, had been 

 ? ound in various formations from the lower oolite 

 upwards. These spines are paddle-shaped, compressed, 

 .ongitudinally grooved, flattened almost into plates, 

 md strongly serrated on the edges. In the nummu- 

 dtic beds of Val-Dominico near Yerona such spines 

 acre found associated with plates much resembling 

 :hose of Cidaris, but with the unique peculiarity of a 

 cow of holes penetrating the test in the areolar space 

 i-ound the primary tubercle. This character our new 

 Urchin does not possess, but the radioles have the 

 latness, the longitudinal striae, and the serrated edges 



f those of Porocidaris. 



I do not attach much importance to the perfora- 

 ions 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- 



ion 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 

 itest is thin these grooves might readily penetrate the 

 plate, or so nearly penetrate it as to be worn into 

 boles 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 areolge tend to become 

 confluent. 



Scattered plates only of this genus have been 

 Pound fossil, and the ovarial plates were till now 

 unknown. They present a very singular character, 

 which is certainly of generic value. The ovarial 



