31 



almost the whole length; the hlade is then simply leaf-shaped, rather deep with 

 only a little meshwork in the bottom of the blade, and the whole edge closely 

 serrate. This variety leads to the second form of tridentate pedicellariæ (PI. III. 

 Fig. 21. PI. IV. Fig. 7), which may be as long as the first one but much more 

 slender. The valves join in their whole length ; the blade is narrow, deep, without 

 meshwork; the edge is rather thick, the teeth are placed irregularly, not in a 

 single series, along its whole length. (Also in the first form the teeth are placed 

 irregularly). The quite small tridentate pedicellariæ (PI. V. Fig. 3) are very like 

 those of Diadema sa.vatile. 



The ophiceplialous pedicellariæ occur both in the form of claviform and of true 

 ophicephalous ones. The latter are few in number and found only on the test, not 

 on the buccal plates. The valves (PI. V. Fig. 11) are small, without meshwork, the 

 edge sinuate and serrate as usual. The stalk is long and thick; there is no neck. 

 In the claviform pedicellariæ I have never found the head developed. The triphyllous 

 pedicellariæ are essentially like those of Diadema, the shape only being a little 

 dilTerent (Comp. PI. IV. Fig. 23 ol' Ech. diadema); the edge is smooth. — The stalk of 

 the tridentate and triphyllous pedicellariæ is, as in Diadema, constructed of one or 

 two simple rods; in the latter case they are connected by crossbeams. — The spicules 

 (PI. III. Fig. 17) are triradiate, arranged mostly in two (in the abactinal) or three 

 (the actinal tubefeet) distinct longitudinal series; in the abactinal tubefeet they are 

 mostly larger than in the actinal ones. The buccal tubefeet are provided with large 

 fenestrated plates as in Diadema. 



With regard to Ech. desori I quite agree with Döderlein and ue Membre 

 that it cannot be maintained as a distinct species; in its pedicellaria> and spicules 

 it is quite like Ech. calamaris. 



Echinothrix diadema differs markedly from calamaris in regard to pedicel- 

 lariæ and spicules. The tridentate pedicellariæ occur in two forms. The one is large 

 (25 mm. head), without a neck (PI. III. Fig. 9, 14); itlie valves join throughout half 

 the length ol the blade or more, the blade is simply leaf-shaped, rather deep, with a 

 dense meshwork in the bottom; even in the basal part there is such meshwork on 

 either side of the apophysis. The edge is rather thick, serrate in the whole length, 

 the line teeth being placed irregularly; also the edge of the basal part is serrate. 

 (This form has been rather well figured by Agassiz, Rev. of Ech. PI. XXIV 33 — 36). 

 The second form (PI. IV. Fig. 25, 36) is much smaller, c. 08 mm. (head), with a 

 long neck. The valves are wide apart, joining only at the end. The blade is some- 

 what curved, narrow, almost flat, a little widened at the end, with a little meshwork 

 in the lower part. The edge is smooth, and only in the outer part very finely 

 serrate. The triphyllous pedicellariæ (PI. IV. Fig. 23) are like those of Ech. calamaris. 

 True ophicephalous pedicellariæ I have not found; the claviform ones have been 

 figured by de Meijere (Siboga-Ech. PI. XIV. Fig. 2U4). The spicules (PI. III. Fig. 24, 27) 



