112 PEOF. P. M. DUNCATs^'s REVISION OP THE 



Apical system small ; basal plates broad ; madreporite well de- 

 fined ; all radial plates small, excluded, ornamented ; periproct 

 small ; genital foramina deeply cut. 



Ambulacra ratber broad, sunken or not in tbe median line 

 and along tlie poriferous zone ; with numerous rows of small, 

 equal, plain, low primary tubercles, and small secondary tu- 

 bercles, all more or less absent along the median line and aloug the 

 edges of the plates near their upper and lower transverse sutures, 

 but crowded on the plates elsewhere. Sutures grooved, and with 

 pits at the angles, especially in the median lines. Pairs of pores in 

 triplets, made biserial by the adoral pair being near the tuber- 

 cular part of the plates, the other pairs forming a vertical row 

 near the interradial suture. Plates compound, the adoral com- 

 ponent a large primary, the middle a demi-plate, and the aboral 

 a low primary plate. Some tubercles in the poriferous zone. 



Interradia with few and very high coronal plates, with tubercles 

 resembling those of the ambulacra, crowding the surface in hori- 

 zontal rows except near the median and the transverse sutures, 

 which are more or less bare ; the bare spaces and also the masses 

 of tubercles being triangular in outline. Median line sunken or 

 not. Sutures slight, yet broadly depressed ; pits at the angles of 

 sutures minute. 



Peristome variable, decagonal or nearly circular ; branchial 

 incisions small ; ten buccal plates. Perignathic ridges well deve- 

 loped ; processes large, tall, united over a large foramen. 



Spines short and slender, shortest and tapering abactinally. 



Dowelling of the plates distinct, near the free surface, and in 

 lines passing into tbe test. Blocking out of some ambulacral 

 plates occurs during growth. 



Becent. Japan, East-Indian Islands, Philippines, Navigators, 

 Tasmania. 



Grenus Ambltpnetjstes, Agassiz, 1841, Monogr. Ech. viv. etfoss., 

 Valentin, Anat. Gen. Ech., Preface, p. 9. Desor, 1858, 

 Synopsis, p. 110. A. Agassiz, 1874, Revision, p. 478. 

 J. Bell, 1880, ProG. Zool. Soc. p. 435, pi. xli. figs. 4-6. 

 Duncan, 1883, Jotirn. Linn. Soc. vol. xvi. p. 354; and 1888, 

 Ann. Sf Mag. Nat. Hist. ser. 6, vol. i. pi. xi. fig. 13, p. 116. 

 Test thin, moderate in size ; circular or slightly pentagonal in 



tumid ambital outline, globular or prolate spheroidal. Coronal 



plates numerous. 



