244 HAWAIIAN AND OTHER PACIFIC ECHINI. 



a group of closely related forms, whose extremes are very different from 

 Spatangus yet with which genus they are apparently rather clearly connected. 

 The Challenger took Gonimaretia tylota at her stations 191 and 192, near 

 the Kei Islands in 129-800 fms. on muddy bottoms. So far as I know, it has 

 not been met with since. 



Gonimaretia laevis, sp. nov. 

 Plates 149, figs. 1-3; 161, figs. 5-7. 



Length 24-32 mm.; width 20-27 mm.; height, 12-16 mm. The largest 

 specimen is relatively a trifle wider than the others, but the difference is very 

 slight. The outline of the test is slightly ovoid (PI. 161, figs. 5, 6) ; it is highest 

 just back of the middle and slopes more anteriorly than towards the back (PI. 161, 

 fig. 7). The apical system is slightly anterior and very compact, with three 

 large genital pores (PI. 149, fig. 1; 161, fig. 6). The characteristic form of the 

 petals with the arrangement of the pore-pairs is well shown in the photograph 

 (PI. 161, fig. 6). The asymmetry between petals II and IV is indicated but 

 it is not quite so marked as in the preceding species, although more abundant 

 material might emphasize it. In the largest specimen (PI. 161, fig. 6) there 

 are 13 large pore-pairs in the posterior series of petal II while there are 15 in 

 the same series of petal IV; in the anterior series there are 5 pairs in petal II but 

 only 4 in petal IV; the anterior series forms an angle of about 45° with the pos- 

 terior series at the tip of the petal. The completion of the petals seems to occur 

 late in growth for in neither of the two smaller specimens is there any anterior 

 series of large pore-pairs; in one specimen there is one such pair just indicated 

 at the tip of the petal, and in the other, two pairs can be distinguished as larger 

 than the others. In the posterior petals, the three specimens are nearly alike 

 with 11 or 12 pore-pairs in the inner series and 13 or 14 in the outer. 



The posterior end of the test is truncate with the periproct near its upper 

 margin (PI. 149, fig. 2). The periproct is wider than high and even its lower 

 margin is very little depressed. The subanal fasciole is very distinct and the 

 enclosed plastron is slightly convex; there are 4 ambulacral plates with 3 large 

 tube-feet included on each side; the upper half of the plastron is nearly verti- 

 cal but the lower slopes rather markedly towards the mouth. The bare ventral 

 ambulacra and the long, narrow, sternum fully covered with tubercles is well 

 shown in the photograph (PI. 161, fig. 5) but the peristome and labrum appear 

 more clearly in the drawing (PI. 149, fig. 3). It is worthy of note that the 



