478 AMBLTPNEUSTES. 



pentagonal, adjacent, excluding completely the small triangular ocular plates 

 from the anal system. Madreporic genital much larger than the others. In 

 both the median ambulacra! and interambulacral spaces the bare part of the 

 test is sharply separated from the tuberculiferous part of the plate which 

 occupies about half the outer part. Each plate in the interambulacral 

 space carries two nearly horizontal rows of tubercles, one of primaries, 

 and one above it of secondaries; below the ambitus the secondaries are 

 much smaller in proportion than above the ambitus. The arrangement of 

 the tubercles is the same in the ambulacral space, where of course the 

 horizontal rows are shorter, and in quite large specimens there are not 

 more than from two to three tubercles in each row. The pores at the angles 

 of the plates in the median line of both areas are small, but sharply cut. 

 The tubercles of both areas are of the same size, and both above and below 

 the ambitus the primaries and secondaries are remarkably uniform in 

 size. The pores at the angles of the plates between the poriferous zone 

 and the interambulacral plates are not as well defined as the median pores. 

 The whole bare si>ace of both areas is finely granular. This genus seems 

 intermediate between the Tcmnopleuridae proper and Amblvpneustes, which 

 forms the passage between the sculptured and pitted Ecbinidae to the Echini- 

 dae proper. 



Japan ; Philippine Islands ; Sandwich Islands. 



AMBLTPNEUSTES. 



Amblypneustes Agass., 1841, Mon. Scut. 



Abactinal axis as long as the transverse, sometimes even greater; test 

 extremely thin; abactinal system small, compact, but epiite prominent; ac- 

 tinostome small, without cuts. Poriferous zones broad, forming vertical rows 

 or short trigeminal arcs of well-defined pores. Ambulacral zone broad ; tuber- 

 cles of both areas identical in size ; median spaces frequently bare ; pores 

 very slender and comparatively small ; auricles delicate ; there are frequently 

 sutural pores at the angles of the plates in both areas; spines very fine, 

 slender, short, far apart ; no regular ambitus ; outline more or less ovoid ; 

 auricles slender, tall, scarcelj- touching over the large auricular foramen ; 

 high connecting auricular ridges. 



