78 



depression; no ocular plate reaches the periproct. Along the inner edge of the ge- 

 nital plates there is a close ring of tubercles; one tubercle on each ocular plate. 

 The periproct is covered by very small, rounded plates, all of the same size; the 

 anal opening is central. 



The buccal membrane shows the quite unique feature that there are only 

 five buccal plates and tentacles; the plates are small, round, green. In the inner 

 border of the buccal membrane, close around the mouth, there is a narrow ring 

 of small, rather thick, greenish plates; all the rest of the buccal membrane is 

 naked, with a few bihamate spicules. The gills are small, with the usual, irregular 

 fenestrated plates. The moulhslits are very small and indistinct. The auriculae are 

 connected and very variable in shape. The diameter of the peristome is rather large: 

 45 mm. in a specimen of 12 mm. diameter, 42 mm. in a specimen of 10 mm. dia- 

 meter — c. 37 — 42"''o of the diameter of test. 



Pedicellariæ. The globiferous pedicellariæ (PI. VI. Fig. 35. PI. VII. Fig. 10) 

 have an unpaired lateral tooth almost as large as the endtooth; the blade may be 



quite open or with a more or less broad 

 crossbeam over the inner side. The outer cor- 

 ners are rather sharp but not produced. The 

 glands are double — as usual among the Temno- 

 pleurids. The ophicephalous pedicellariæ have 

 a short neck; the blade is rather short, with- 

 out meshwork, only with a median keel; the edge 

 is a little sinuous and distinctly serrate (PI. VII. 

 Fig. 48). Tridentate pedicellariæ I have not 

 found. The triphyllous pedicellariæ (PI. VI. 

 Fig. 43) are very small, a little elongate, with 

 smooth outer edge. The sphæridiæ are placed 

 at the pits of the 5 — 6 inferior plates. The 

 spicules are extremely scarce; in the tube feet 

 and the internal organs I have found none, 

 only in the buccal membrane a few bihamate 

 ones have been found. 



The spines (Fig. 6) are short and slender, 

 c. '/a of the diameter of the test (in larger spe- 

 cimens); they are a little thorny in the outer 

 jiart, the point not swollen, ending in a central 

 thorn with a circle of points around, all small 

 and rather indistinct. The actinal spines are 

 not curved or widened at the end. 

 The colour of the test is green with some irregular white spots, and some- 

 times a reddish tint in the median part of the interambulacral areas. The edge 



J^ 



Fig. fi. 



Fig. 7. 



Fig. (i. 



Fig. 7. 



Tlie point of a secondarj' spine of 



Pleiirecliiims scillœ (Seibert. Obj. 



II. Oc. III). 



The point of a primary spine of 



I'lenrechinus Dödericini. (Seibert. 



Obj. (J. Oc. 0. 1 



A primary spine of Pleurerhimis 



siamcnsis. (Seibert. Obj. II. Oc. III.) 



