174 BULLETIN 100, UNITED STATES NATIONAL MUSKUM. 



AMPHIOPLUS IMPRESSUS (Ljungman). 



Plate 64, figs. 3, 4. 



Amphipholis impressa Ljtjngman ('66), p. 314. 

 Amphiura impressa Lyman ('82), p. 148. 

 Amphioplus impressa H. L. Clabk ('15), p. 258. 



Localities. — Albatross station 5369; Marinduque Island and vi- 

 cinity; Tayabas Light (outer) bearing N. 50° W., 16.30 kilometers 

 (8.8 miles) distant (lat. 13° 48' 00" N., long. 121° 43' 00" E.) ; 

 194 meters (106 fathoms) ; February 24, 1909; bk. S. 



One specimen (Cat. No. 41170, U.S.N.M.). 



Albatross station 5371; Marinduque Island and vicinity; Tayabas 

 Light (outer) bearing N. 43° W., 11.1 kilometers (6 miles) distant 

 (lat. 13° 49' 40" N., long. 121° 40' 15" E.) ; 152 meters (83 fathoms) ; 

 February 24, 1909; gn. M. (m. b.). 



One specimen (Cat. No. 41171, U.S.N.M.). 



Notes. — The diameter of the disk in the two specimens is 8 mm. and 

 6.5 mm. respectively; the arms are incomplete in both; one of the 

 arms of the smaller may have had a length of about 37 mm. or 38 mm. 



The disk is rounded, slightly convex on the two surfaces, with the 

 borders thin. The dorsal surface is covered with rather large and 

 stout plates, especially in the central region, which become smaller 

 toward the periphery; these plates are polygonal, rounded, and 

 slightly imbricated. A central rosette of rounded primary plates, 

 all of the same size and scarcely larger than the neighboring plates, 

 may be with difficulty distinguished ; the radials are in contact with 

 the dorsal central plate, but are separated from each other by a nar- 

 row plate. At the periphery of the disk there may be distingushed 

 a very marked bordering made up of rectangular plates which are 

 broader than long. All these plates bear on their surface extremely 

 fine striae which are irregularly sinuous, recalling the striae of the 

 madreporic plate of a starfish, but very much finer and less evident. 

 The radial shields are elongated, three times as long as broad, with 

 the external border convex, the internal border straight, and the 

 proximal angle sharp; the two shields of each pair are in contact 

 through three-quarters or four-fifths of their length, and they are 

 separated inwardly by a small triangular plate. The surface of these 

 shields shows striae similar to those of the other plates of the disk, 

 but these striae are much broader and deeper, and consequently more 

 evident. 



The ventral surface of the disk is covered with small, subequal, 

 polygonal or rounded, and slightly imbricated, plates. The genital 

 slits are very narrow. 



The mouth shields are lozenge-shaped, a little longer than broad in 

 the larger specimen, and almost as long as broad in the other; the 



