568 MARETIA. 



scarcely wider than the actinal plastron. The anal system is transversely 

 elliptical, proportionally much smaller than in S. purpureus, and is placed 

 near the ambitus ; the arch of the abactinal part of the posterior interambu- 

 lacrum reaching nearer the ambitus than in S. purpureus, in which the trun- 

 cated extremity of the posterior end is much larger. 



The small tubercles covering the abactinal surface are smaller and more 

 closely crowded than in S. purpureus, extending over the anterior groove ; 

 the miliaries are larger, consequently the spines which cover the abactinal 

 surface are more uniform in appearance. The same is the case on the ac- 

 tinal surface; the tubercles increase greatly in size, bul are not so large as 

 in S. purpureus, either adjoining the bare ambulacra or in the actinal plas- 

 tron. The color of the smaller spines of dried specimens is dark violet; the 

 large spines are lighter-colored. 



German Ocean; Azores. 



(SPATANGUS.) Maretia. 



Maretia Gray, 1855, Cat Bee. Ech. 



Test thin, flattened ; large tubercles upon the interambtilacral areas, ex- 

 cept the oild one. Actinal plastron smooth, destitute of spines. No fascioles 

 except a subanal one. which is more or less indistinct. Petals spreading, at 



same time elongate, extending nearly to the ambitus. Anterior groove in- 

 distinct, it disappears entirely on the abactinal surface. 



This subgenus is distinguished from Spatangus proper by the great devel- 

 opment of the bare posterior ambulacral spaces of the actinal side, the small, 

 nearly smooth, actinal plastron, the thin flattened test, and different mode 

 of arrangement of the primary tubercles. None of these characters are, 

 however, features which seem to entitle Maretia to rank as anything more 

 than a subgeneric division of Spatangus. Desor has distinguished as Ilcini- 

 patagus, tertiary Spatangoids agreeing in every respect with the present 

 generic division formerly established by Gray, from the single recent species 

 known at that time. 



