194 RECENT OPHIURANS. 



200. O. PACHYBACTRUS H. L. Clark, 1911. Bull. 75 U. S. N. M., p. 242, f. 116. 



2 specimens. Aleutian Islands: off Agattu, 482 fms. 



201. 0. PACHYPHYLAX, sp. nov. (iraxOs, fat + 0uXa£, guard.) Plate 2, f. 8, 9. 



Disk, 9 mm. in diameter; arms five, about 20 mm. long. Disk well covered 

 by low stumps, crowned with 4-6 minute spinelets. Radial shields narrow, 

 somewhat concealed, but indicated by a pair of elevated, widely separated, 

 parallel ridges at the base of each arm; at the distal end these may be quite bare. 

 Upper arm-plates, rather small, rounded triangular, widely separated. Inter- 

 brachial spaces below, covered by numerous minute granules. Genital slits 

 long and conspicuous. Oral shields small, diamond-shaped, rather wider than 

 long. Adoral plates large, somewhat curved, nearly twice as long as wide. 

 Oral papillae 5 or 6 on each side; the two distalmost are short, thick and elhp- 

 soidal and stand on the outer, proximal corner of the adoral plate, guarding the 

 large oral tentacle-pore (hence the name) ; of the remaining 3 or 4 papillae, the 

 most proximal is largest but is somewhat smaller than a tooth, while the most 

 distal is smallest and stands just within or above the fii-st of the stout papillae 

 protecting the oral pore. First under arm-plate rather large, rounded hexag- 

 onal; succeeding plates more or less pentagonal with rounded distal margin, 

 at first wider than long, but becoming longer than wide distally; basally they 

 are more or less in contact with each other. Side arm-plates rather large, 

 meeting broadly above, even at base of arm, but more narrowly below and bas- 

 ally they are usually separated by the under arm-plates; each side arm-plate 

 carries seven spines of which the uppermost is longest and exceeds two joints; 

 it is smooth, terete, opaque; the three following are similar but successively 

 shorter; the three lowest spines are abruptly smaller, subequal, blunt, and 

 thorny. Tentacle-pores srnall; tentacle-scale single, small, more or less spini- 

 form. Color (dried from alcohol), dirty whitish, disk somewhat darker. 



HoLOTYPE (M. C. Z. 2128). East of Nantucket, 524 fms. Blake 

 St. 306. 



This specimen was not identified by Mr. Lyman but with it is a note in his 

 handwriting: "0. anomala has 6 arms, this 5 and 1 more m. papilla than type. 

 Also arm-spines more thorny." It seems to find its nearest ally in 0. trachy- 

 bactra from Bering Sea, which it resembles very closely except in the mouth- 

 parts. In the curious pair of short, stout papillae standing guard over the 

 oral tentacle-pore, this species is different from any ophiacanthid yet described. 

 It is obviously not a typical Ophiolebes but it certainly belongs in the genus 

 as used in the present paper. 



