NO. 2 ZIESENHENNE : NEW OPHIURANS 33 



been selected because of the difficulty of distinguishing this species from 

 other Pacific forms. 



OPHIODESMUS, new genus 



Similar to Ophionereis, but the disk scaling is coarse and compacted 

 to such a degree that only a small portion of some of the disk scales is 

 visible. The supplementary arm plates are very small, confined mainly to 

 the side of the arm and not conspicuous from above. Upper arm plates 

 oval, slightly wider than long. This genus seems to be a connecting link 

 between Ophionereis of the Ophiochitonidae and Ophiactis of the Amphi- 

 uridae. Since it shows characteristics of both families and the under side 

 is decidedly similar to Ophionereis, this genus is placed in the Ophiochi- 

 tonidae. The name Ophiodesmus has reference to its connecting-link po- 

 sition between Amphiuridae and Ophiochitonidae. 



Genotype: Ophiodesmus aniphilogus, new species. 



Ophiodesmus amphilogus, new species 

 Plate 9, Figs. 4-6 



Description. — Disk diameter, 4.5 mm. ; arms, short and slender, grad- 

 ually tapering, about 11 mm. long. Disk circular and flat, covered by 

 numerous compacted, overlapping, irregular scales. Some of the scales are 

 compacted and overlap to such an extent that only an elliptical portion or 

 narrow margins are exposed. Surrounding the larger scales are several 

 irregularly placed smaller scales. There are 7 to 9 irregular series of 

 scales in each interradius. Primary plates are not conspicuous. Radial 

 shields small, oval shaped, about twice as long as wide, widely separated, 

 about their length apart, by several large and numerous small disk scales. 

 Length of shields about 54 of the disk radius. 



First upper arm plate small, wider than long, distal margin convex. 

 Second plate oval shaped, larger than the first, slightly wider than long, 

 distal margin strongly convex. Third and succeeding plates larger, oval 

 shaped, basally wider than long, distally becoming longer than wide, mar- 

 gins convex. Basally the plates overlap; distally they become separated by 

 the side arm plates. Under high magnification the upper arm plates appear 

 smoother in texture than the side arm plates. Side arm plates wider than 

 long, spine ridge produced and prominent, bearing 3 heavy, flattened, 

 broad, short, subequal arm spines, as long as an arm segment basally, and 

 gradually reducing in length distally to the arm tips where they are 



