128 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



process separating the mouth shield from the first side arm plate. 

 The oral plates are triangular, a little higher than broad. The lat- 

 eral mouth papillae, three in number, are subequal and conical, with 

 the point blunted; their surface is very rugose and provided with 

 small and very closely crowded asperities. The unpaired terminal 

 papilla is a little stouter than those on either side. 



The upper arm plates are rather small, triangular, broader than 

 long, with a sharp proximal angle, two straight sides, and an almost 

 straight distal border passing into the preceding by rather sharp 

 angles. All these plates are separated from the base of the arms 

 outward by an interval which is occupied by the side arm plates. 



The first under arm plate is elongated, with a very convex distal 

 border, which is broader than the straight proximal border. The 

 following plates are very broad, pentagonal, with an obtuse proxi- 

 mal angle bounded by two straight sides, two sides slightly exca- 

 vated by the tentacle scale, and a very broad strongly convex distal 

 border. Beyond the disk these plates become a little less broad, and 

 they end by being as broad as long; they are separated beyond the 

 second by a rather long interval occupied by the side arm plates. 

 On the surface of these plates and in their distal half there may be 

 made out a few parallel striae, which are, however, but little marked. 



The very strongly projecting side arm plates carry at the base of 

 the arms 10 arm spines; the two lateral columns come very close 

 together in the median line, though without being continuous. The 

 length of the spines increases from the first ventral, which is equal 

 to a segment and a half, to the last dorsal, of which the length equals 

 two and a half or three segments. These spines are large and strong, 

 with their tips rounded and their surface very rugose; the ventral 

 spines even show very fine and closely placed asperities, which, how- 

 ever, are not worthy of the name of teeth. 



The single tentacle scale is rather large, elongated, and oval, with 

 the extremity obtuse or rounded ; its surface is very rugose and its 

 border even shows more or less marked fine asperities. 



In the alcoholic specimen the disk has a brownish-yellow color, 

 very light on the dorsal surface, and the arms show light-brown an- 

 nulations separated by longer uncolored portions. To judge from 

 the coloration, O. suspectus must have come from shallow water. 



Affinities and distinctive features. — I have been much puzzled in 

 placing generically this unique specimen, which I have called 

 Ophiophthalmus suspectus, for it shares in its characters both the 

 characters of the genus Ophiomitrella and those of the genus 

 Ophiophthalmus, the first considered in the restricted sense given 

 it by Matsumoto. It recalls this genus in the two lateral series of 

 arm spines, which come yery close together in the dorsal median 



