232 HAWAIIAN AND OTHER PACIFIC ECHINI. 



Gymnopatagus obscurus. 



A. Agassiz and Clark, 1907. Bull. M. C. Z., 60, p. 254. 



Plate 158, figs. 1-4. 



Length 85 mm.; width across anterior petals, 58 mm.; across proximal 

 part of posterior petals 67 mm.; across distal part of posterior petals, 70 mm.; 

 height back of apical system 35 mm. The form of the test will be easily under- 

 stood from the photographs (PI. 158, figs. 1-3) while the picture of the bare 

 test (PI. 158, fig. 4) reveals the petals, the tuberculation and the four genital 

 pores. The depression of ambulacrum III is so slight that it is only in a bare 

 test that it becomes evident. It will be noticed that the large primaries of inter- 

 ambulacrum 5 are confined to the neighborhood of the tips of the petals. The 

 periproct is large, 11 mm. wide by about 9 mm. high, and occupies most of 

 the vertical portion of the posterior end of the test; below it lies the slightly 

 convex but very oblique subanal plastron, into the composition of which 4 

 ambulacral plates (with 3 large tube-feet) on each side, enter. As will be seen 

 from the figure (PI. 158, fig. 2) the sternum is relatively long and narrow (as 

 compared with pulchellus for example, PI. 159, fig. 4) and the peristome is nearly 

 circular. The labrum is relatively short and wide, its greatest width being about 

 one half its length. The peripetalous fasciole shows a marked tendency to 

 become double in places and in one specimen, it is more or less double or branched 

 for the greater part of its course. At the tips of the anterior petals, it is particu- 

 larly apt to be double. The primary spines are neither as long nor as conspicu- 

 ous as in pulchellus and magnus; some of them are whole and are not 20 mm. 

 long, and are very slender. The general color of this species is dull brown, 

 the spines somewhat lighter. 



The pedicellariae are remarkably similar to those of pulchellus, but the tri- 

 dentate are of a more uniform type, with narrow valves, basally compressed 

 and distally expanded; the apophyses are very deep and conspicuous; the 

 valves are .40-1.00 mm. in length. Ophicephalous and triphyllous pedicellariae 

 are of the same size and form as in pulchellus. The rostrate are all of the ordi- 

 nary type and the valves are only .30-.45 mm. long. No globiferous pedicel- 

 lariae were seen. 



This species is remarkably near to the Japanese species micropetalus in 

 the form <>t the test, the appearance of the posterior petals ami the composition 

 «.t the aubanal plastron. But it differs markedly in the anterior petals, the 



