No.1749. A SEW EUROPEAN CRIXOID— CLARK. 331 



The anal plate is the only interradial which has been observed in 

 the two Mediterranean species of the genus Antedon; but Wyville 



Thomson observed "in one or two cases * * * about the time 

 of the first appearance of the anal plate a series of five minute 

 rounded plates developed interradially between the lower edges of 

 the anal plates and the upper edge of the basals." The appearance 

 of live interradials in Antedon bifida is exceedingly interesting, for it 

 shows an approaeli to the conditions found in the highly specialized 

 family Comasteridie, in which they are always, so far as known, 

 highly developed in the young, and to the conditions found in the 

 equally specialized family Pentametrocrinidae, in which they were 

 described in the young of one of the species of Pentametrocrinvs 

 ("Tha Hlltatocrinus ,, ). 



I have recently shown that Antedon is primarily an Indian 

 Ocean genus, an intrusion into the Atlantic area, like Leptometra. 

 The area inhabited by it is marked by a series of species each phylo- 

 genetically more developed than its predecessor, and the least special- 

 ized more advanced than the species of Maslhjometra, its modern 

 representative in the Indian Ocean. 



The hitherto undescribed Antedon from the Adriatic Sea may be 

 appropriately known as: 



ANTEDON ADRIATICA, new species. 



Centrodorsal flattened hemispherical, about 4 mm. in diameter at 

 the base, the bare dorsal pole flat, about 1.5 nun. in diameter; cirrus 

 sockets arranged approximately in three closely crowded alternating 

 rows, the uppermost of which includes about four sockets in each 

 radial area. 



Cirri XXV-XL (usually XXX-XXXV) 22-30 (usually 24-28), 

 20 mm. to 27 mm. long, slender, and of uniform thickness throughout 

 their length; first segment very short , the second about half again as 

 broad as long, the third about as long as broad, the fourth half again 

 as long as the width of its expanded ends: fifth and following about 

 twice as long as the width of the distal ends, and remaining of prac- 

 tically the same proportions to the end of the cirrus, though the 

 distal segments may be a trifle shorter than those nearer the base; 

 penultimate segment nearly or quite twice as long as broad, and 

 bearing a prominent slender and sharp opposing spine which is sub- 

 terminal in position, directed slightly forward or nearly erect, and 

 equal to about one-half the distal diameter of the penultimate seg- 

 ment in height. Terminal claw slender, evenly tapering, and moder- 

 ately and uniformly curved, about equal to the penultimate segment 



a They have been described in the young of Comatilia, and they arc equally well 

 developed in the pentacrinoids of Comactinia meridionalis. 



