12 BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



STENOMETRA SNELLIUSI A. H. Clark 



PLATE 1, FIGURE 1 



Stenometra snelliusi A. H. CLARK, Temminckia, vol. 1, 1936, p. 295 (listed), p. 313 (description; 

 Snellius station 253*), pi. 8, fig. 9. 



Diagnostic features. The elements of the division series and first two brachials 

 have the proximal and distal borders swollen and irregular, though not especially pro- 

 duced, more or less tubercular or armed with scattered spines, and the lateral borders 

 with a conspicuous development of short spines; and there are no supplementary 

 dorsolateral processes on the earlier brachials. The 20 arms are 70 mm. long, and the 

 cirri are 35 mm. long with 68-75 segments. 



Description. The centrodorsal is a short thick column about twice as broad as 

 high, 3 mm. in diameter. The dorsal pole is concave and bears scattered and irregular 

 more or less spinous or pointed tubercles. The cirrus sockets are arranged in ten 

 crowded columns of two each. 



The cirri are XX, 68-75, 35 mm. long. The first segment is about four times as 

 broad as long and those following slowly increase in length to the seventh and eighth, 

 which are from one-third to one-half again as long as broad. The tenth, eleventh, or 

 twelfth is a transition segment, and is slightly longer than broad. The segments fol- 

 lowing continue to decrease in length so that those in the distal third of the cirri are 

 very short, about two and one-half times as broad as long. On the segments following 

 the transition segment the median portion of the distal dorsal edge gradually becomes 

 more and more prominent, involving progressively more and more of the dorsal surface, 

 so that the very short distal segments bear each a very high carinate spine. The earlier 

 segments as far as the transition segment have their distal edge all around produced. 

 Up to about the twelfth-fifteenth the segments have the middle of the ventral distal 

 edge produced into a more or less conspicuous tooth. The cirri taper from the base to 

 about the seventh segment, then much more slowly, and again more rapidly at the tip. 



The radials are concealed in the median line, but are visible as broad low triangles 

 in the interradial angles. Their edges are swollen and produced, and are irregular, 

 more or less tubercular, and armed with scattered spines. The IBri are about five times 

 as broad as long, with the edges all around produced, and the distal and lateral edges 

 sparsely spinous. The IBr 2 (axillaries) are rhombic, twice as broad as long, with the 

 edges everted and sharply, coarsely, and very irregularly serrate, except near the mid- 

 radial line, and the lateral angles very deeply and sharply serrate or spinous. The 

 elements of the IBr series bear very high thin median keels with the crest finely or 

 coarsely and irregularly serrate, or deeply notched. The IIBr series resemble the 

 IBr scries, but the proximal, distal, and inner borders of the ossicles are somewhat 

 less spiny or irregular, while the outer borders, on the outside of the postradial series, 

 bear numerous long, slender, and irregular spines. The crest of the high median 

 carination is usually smooth, but may be finely serrate, or even coarsely dentate. 



The 20 arms are 70 mm. long. The first brachials are about three times as broad 

 as the median length, and are slightly longer exteriorly than interiorly. Their edges 

 are narrowly everted and are usually smooth, except that the outer side of the outer- 

 most first brachial on each postradial series is coarsely and irregularly spinous. The 

 second brachials are irregularly five sided. The inner side is about half as long as the 

 outer, and the proximal border forms an obtuse angle with the apex in the median line. 



