394 POROCIDARIS. 



aries between the outer rows of secondaries. Scrobicular circles ill defined, 

 running into one another along the middle of the horizontal lines of contact. 

 Broad median interambulacral zone. Secondary tubercles gradually diminish- 

 ing in size towards centre of median space, tilling edge of coronal plates 

 between scrobicular circles and the poriferous zone. Secondary spines elon- 

 gate, yellowish, with green stripe along the middle, tipped with pink. Ambu- 

 lacra] secondaries dark green. Primary spines flattened, tapering, with very 

 marked serrated edges, and smaller spines along median line of shaft of 

 spine; this is irregularly banded and spotted with violet, upon a greenish- 

 yellow background. Color of collar of spine violet-brown, with white spots. 

 Granulation of spines irregular, with longitudinal lines of larger granules, 

 alternating or mixing in witli smaller granulations. Plates of buccal mem- 

 brane small, closely packed together. Primary tubercles small; mammary 

 boss little prominent; auricles very high and thin. 



Australia; East [ndia [glands. 



POROCIDARIS. 



Porocidaris Ues , 1851. Syn. Ecli. fuss., p. 46. 



Among the most interesting genera collected by the Porcupine Expedition 

 is ;i recent representative of tins genus, hitherto only known from isolated 

 coronal plates, and from spines fully bearing out the characters and pecu- 

 liarities upon which tliis genus bad been established. The coronal plates are 

 pierced round the scrobicular circles by pores situated in shallow furrows 

 radiating round the scrobicular circle ; associated with these isolated fossil 

 plates, we find peculiar spines, remarkable for their flattened form, longitudi- 

 nally plicated, with strongly serrated edges. Milled ring prominent ; collar 

 distinct. In the recent specimens these flattened serrated spines were 

 found to occur round the actinostome. The primary spines of the test 

 above the actinostome are long, swollen at the base, tapering, and re- 

 markable for the immense development of the collar, which extends fre- 

 quently half the length of the shaft of the spine. Other spines are more 

 cylindrical, all are finely granular, presenting a tolerably smooth Burface. 

 The collar is of a beautiful brilliant purple, according to Professor Thomson; 

 and from this he has named the species mentioned below. 



