112 BULLETIN 82, CTNTTBD STATES NATIONAL MUSEUM 



amined, when the perfectly Btraighl and uniform fine dotted lino indicating the 



presence of a syzygy identifies it at once. The long, Blender, and sharp dorsal spines 



on the outer cirni uts and the dark ventral saddle-shaped patches commonly 



■it on the oirrufi Begments also serve to distinguish it at a glance from any similar 



Bpeciee of Heterometra. 



1 1. tcripti m The centrodorsal is discoidal, broad, with a broad, flat, or slightly 

 concave dorsal pole 5-6 nun. in diameter. The cirri are arranged in usually two 

 irregular ami closely crowded marginal rows. 



The cirri are X XXXII (usually about XX), 25-45 (usually 29-35), 15-35 (usually 

 between 20 and 30) mm. long. The first segment is about twice as broad as long and 

 those following increase gradually in length to the fourth or fifth, which varies from 

 about as long as broad to one-third or even one-half again as long as broad. The 

 three or four segments following are similar, and those succeeding gradually decrease 

 in length so that the terminal seven or eight are nearly twice as broad as long. From 

 the sixth to the eighth there is a more or less marked transition segment that does not 

 decrease in width distally, and is seldom with any indication of a dark band. From 

 the sixth-thirteenth (usually seventh-ninth) segment onward long sharp dorsal spines 

 are developed. The opposing spine is long and slender, and is about as long as the 

 penultimate Begment. The terminal claw is considerably longer than the penultimate 

 segment, and is rather slender and moderately curved. The longer proximal segments 

 have a slight central constriction. 



The distal ends of the rndials are visible beyond the rim of the centrodorsal. 

 They are usually plain, but in western specimens may be obscurely beaded. The 

 postradial series resemble in general thoso of Z. elegans but are relatively somewhat 

 longer. The sides of the dnision series, which are usually in close lateral contact, 

 may he sharply flattened with a distinct dorsolateral line, or they may be barely in 

 contact. The sides of the division series are usually smooth, but occasionally they 

 a few irregular spinous processes. The IIBr series are usually all 4(3+4), but 

 one or more may be 2, and in rare cases half, or even the majority, may be 2. The 

 IIIBr series are most frequently all 2 and are usually developed oidy internally so that 

 commonly the arms on each postradial series are six in number and are arranged in 

 I, '_'. 2. 1 order; but IIIBr 4(3 + 4) series are not infrequent, and in rare cases half, or 

 e\ cm the majority, of the IIIBr series may be 4(3+4). IVBr series are rarely devel- 

 oped, bui occasionally one is present, and in one case two were present in a single 

 individual. They are 4(3+4); but in the individual with two, one was 4(3+4) and 

 the other was 2. 



The arms are 14-41 (averaging about 25) in number and are 40 to 135 (averaging 

 about 85) mm. long. They are usually of moderate length and moderately tapering, 

 but they may be slender and taper very slowly. The brachials are rather short, in 

 tli.' proximal portion of the arm wedge-shaped and distally oblong; they are some- 

 times very short, as in the genus Ifimerometra. The brachials after the fourth or fifth 

 have Btrongly produced and very finely spinous distal edges, making the arms very 

 rou^h to the touch. 



The pinti mble those of Z. elegans but have fewer segments. 



The ambulacra of the disk are very strongly plated and the interambulacral 

 areas, especially the anal area, are also more or less strongly plated. 



