182 HAWAIIAN AND OTHER PACIFIC ECHINI. 



of the abactinal side are curved downward toward the ambitus from the 

 outer edge of the interambulacral zone to the median line (PI. 73, fig. l) all 

 the way from the abactinal system to the ambitus (PI. 75, fig. £). The same 

 is the case with the ambulacral plates to a limited extent, only the plates 

 about one-third of the way from the ambitus towards the abactinal system 

 being curved towards the median ambulacral line (PI. 73, fig. i), those nearer 

 the abactinal system being only slightly curved or horizontal (PI. 75, fig. £). 



At the ambitus the ambulacral and interambulacral areas are of nearly 

 the same width (Pis. 73, 74). On the abactinal side the interambulacral 

 areas are bordered along the ambulacra by a more or less regdlar vertical 

 series of small primary tubercles flanked near the ambitus by a shorter 

 row of similar tubercles extending on five or six interambulacral plates. 

 The rest of the interambulacral plates are for the most part covered with 

 distinct small secondaries and miliaries, but along the median interambu- 

 lacral line are found two rows of small primaries extending from the actinal 

 side to the abactinal side of the ambitus. These rows are well seen in the 

 profile view of the test (PI. 73, fig. 2). On the abactinal surface, in the 

 median ambulacral area, occur two or three irregular vertical series of small 

 distant primaries and secondaries extending from the ambitus to the abac- 

 tinal system. The poriferous zones on the abactinal surface occupy two- 

 thirds of the ambulacral area ; the two vertical inner rows of pairs of pores 

 are well separated from the single outer line (PI. 75, fig. ji). 



On the actinal side the poriferous zones approach the outer edge of the 

 ambulacra and at the actinostome are closely packed (PI. 75, figs, i, 3). On 

 the actinal side of the test (PL 74) the interambulacral plates are of uniform 

 height, sharply inclined towards the median line ; only the nine or ten plates 

 nearest the actinostome are separated by uncalcified membrane. The verti- 

 cal series of interambulacral primaries next the ambulacra are regular and 

 prominent (PI. 74), while the less marked rows of similar tubercles on each 

 side of the median interambulacral line are not very noticeable. The 

 actinal system is about 35 mm. in diameter and has prominent gill cuts. 

 There are twelve to fourteen rows of narrow imbricating plates between the 

 teeth and the ambulacral coronal plates (PI. 75, fig. 1), which carry second- 

 aries arranged in horizontal rows. 



The abactinal system (PI. 75, fig. 2) is from 20 to 25 mm. in diameter. 

 The genital plates are pointed and much elongated with the genital open- 

 ings placed in the proximal part of the genital membrane, which carries 



