148 HAWAIIAN AND OTHER PACIFIC ECHINI. 



Argopatagus planus. 



Mi ijerea plana A. Agassiz and Clark, 1907. Bull. M. C. Z., 61, p. 132. 



Plate 151, figs. 6-8. 



Length 28 mm.; breadth in front of abactinal system, 22 mm.; height 

 at posterior end, 9 mm. and at anterior end 4 mm. The shape of the thin, 

 fragile tesl will be besl understood from the figures 6, 7 and 8 (PI. 151), which 

 also show clearly the tuberculatum. The abactinal system is a little back of 

 the middle of the test; it is small and compact and there are no genital pores 

 visible; even the ocular pores are hard to detect. The labrum is narrower 

 than in ritreus and has a nearly straight anterior margin; it carries a very few 

 small tubercles near the mouth. There is considerable tuberculation about 

 the ambitus but there is nothing like a true marginal fasciole. The subanal 

 fasciole is very well developed, not at all angular and encloses a space G mm. 

 wide by 2 mm. high. The periproct is on the vertical posterior surface. The 

 primary spines are all broken but were evidently about 6-8 mm. long, whitish, 

 glassy, and sparsely prickly. Of pedicellariae, I have found only a single tri- 

 dentate, the valves of which are narrow, about half a millimeter long and .06 

 or .07 mm. across the blade, .10-.12 mm. across the base. The color of the 

 test is light brown. 



After comparison with the specimens of vitreus, which are decidedly larger 

 and with the various figures of that species which have been published, it is 

 evident that this unique individual represents a different species. Besides 

 the marked difference in the form of the test, an excellent specific character 

 for planus, to separate it from vitreus, is found in the arrangement of the plates 

 around the peristome, where interambulacra 1 and 4 are completely shut out 

 by the contact of 1M and IIol and of IYM and Vol (PI. 151, fig. 7). This may 

 of course prove to be an individual peculiarity but for the present it may well 

 be considered a good specific character. 



Station 4919. Off Kagoshima Gulf, Japan. Bott. temp. 41.S . 440 fms. 

 Glob. oz. 



One specimen. 



