24 THE VOYAGE OF H.M.S. CHALLENGER. 



angle withiu, l^ounded l^y re-entering curves, and outer edge much rounded ; length to 

 breadth 1.5 : 1.3. Side mouth shields short and thick, vdde without, meeting broadly 

 within. First under arm plate small, pointed, transverse oval in shape ; second plate 

 large pentagonal, with inner angle truncated, lateral sides having a short but deep re- 

 entering curve, and outer edge neatly curved ; the plates beyond have a long sharp angle 

 withiu, and very short lateral sides. Side arm plates wide, and somewhat swollen, and 

 flaring outward, meeting below 'beyond the fourth under arm plate, and above beyond the 

 first ujjper plate, which is much swollen and narrow fan-shaped, with an angle inward. 

 Disk round flat, and rather thin ; in centre a rosette of six large, ii-regular, rounded 

 primary plates, the five outer ones separated from each other by pairs of small, thick, 

 angular scales. In the interljrachial spaces are numerous small, and three large plates in 

 a radiating line, two long hexagonal and one larger and rounded on the margin. Eadial 

 shields somewhat sunken, longer than wide, with irregularly curved outlines, and a blunt 

 angle within and without, separated at their inner end by a large hexagonal plate, and 

 without by a small triangular plate. Lower interbrachial space filled by three transverse 

 rows of irregular plates. Genital scales long and narrow, and composed of several pieces. 

 Two short, stout, blunt pointed arm spines, the upper one longer, and two-thirds 

 as long as an arm joint. One large round tefntacle scale on each pore. Colour in alcohol, 

 white. 



Station 23. — March 15, 1873 ; ofi" Sombrero Island; 450 fathoms; giobigerina ooze. 



Ophiozona depressa, Lym. (PI. XI. figs. 16-18). 



Opinozonadepressa, Lym., Bull. Mus. Comp. Zool. vol. v., part 7, p. 128, pL vi. figs. 155-157, 1878. 



Two nearly equal short arm spines. Arm low. Side arm plates slightly flaring 

 without. Radial shields large, oval, and widely separated. 



Diameter of disk 11 mm. Length of arm about 37 mm. Width of arm close to 

 disk, without spines, 1'8 mm. Four short, squarish, close-set mouth papillse on each 

 side, the outer one very small, and a pair somewhat more pointed at apex of angle. 

 Mouth shields longer than broad, with a sharp angle within, and outer side bounded by 

 a deep curve ; length to breadth 2 : 1 "7. Side mouth shields short, broad without 

 tapering inward, where they meet in a jioint. First under arm plate very small, 

 transverse pointed oval ; next two plates long pentagonal, with a truncated angle 

 within, deep re-entering curve on each inner lateral corner, and a curved outer edge ; 

 beyond these the plates are short pentagonal. Side arm plates low (the arm being flat), 

 little swollen, slightly flaring outward, meeting below beyond the fifth under arm plate, 

 and above beyond the second ujjper plate, which is fan-shaped, with an angle '^\dthin. 

 Disk round and flat ; in the centre is a large pentagonal primary plate, round which 

 are five others, smaller and more or less rounded, separated from each other hj a 

 triangular scale. These primary plates have a little central boss or tubercle ; in the 



