OF NEW SOUTH WALES. 149 



Actinosome. — The central orifice, or mouth, in life covered 

 with a membrane, plates, or spines. 



\bactinal surface — The upper side. 



Ambulacra. — The space included between the two poriferous 

 zones. 



Interambulacra. — The five areas between the ambulacra. 



Ambitus. — The rounded edge of the base on which the test 

 rests. 



Genital plates and ocular plates are sets of five each, with 

 pores at their edge or centre. They are referred to here as the 

 G. and 0. plates. The 0. plates are sometimes without pores. 

 Within these is the anal system, which is composed of one 

 or many plates, and has one anal slit or pore. 



The madreporiform body is a spongy tissue on one of the 

 G. plates. 



To abbreviate references, the ambulacral and interambulacral 

 areas are always referred to as the A. and I. areas. 



Sub-Order 1. — Desmosticha. Hasckel, 1866. 



(The Endocycla of Wright.) 



Echini, more or less circular in outline. Anal system com- 

 pletely surrounded and enclosed by reproductive and ocular 

 plates. Actinosome central. Zones of pores extending from 

 anal system to actinosome in simple vertical rows or disconnected 

 arcs. Jaws highly developed, supported upon prolongations 

 (auricles) of the edge of the actinosome either as arches or dis- 

 connected supports. Five rows of ambulacral and five inter- 

 ambulacral plates only. Tf the test is elongated in form, the 

 longitudinal axis is indicated by the position of the madreporic 

 body. Actinal system covered by a flexible membrane attached 

 to the jaws, either bare, or more or less covered with plates. 

 Gills extending through openings in the edge of membrane, 

 corresponding to cuts more or less marked on the edge of the 

 actinosome. Tubercles carrying the spines form vertical or 



