— 45 — 



Westphalia, (Zittcl : iibcr Coelop. Taf. VI, figs. 16-29) 

 and in the llocene sand of Brussels (Rutot: op. cit. PI. Ill, 

 fig- 9)- 



Quadrifid Spicules of Pachastrella. 

 Pachastrella, sp. 



(Plate ni, figs. 24, 25). 



Simple quadrifid .spicules in which three elongated arms 

 radiate at equal angles from a centre and form the outline 

 of a more or less elevated three-sided pyramid, from the apex 

 of which another arm generally shorter than the other three, 

 extends upwards. There are two very distinct forms of these 

 simple quadrifid spicules. In the larger (fig. 24) the three 

 arms form a very low pyramid ; in some examples they are 

 nearly in the same plane; and the fourth arm, much .shorter 

 than the other three, is near))- at right angles to them. The 

 other three arms are nearly equal, straight and pointed, and 

 in no in.stance which I have noticed are the>- bifurcated at 

 the extremities. Canals are shown in some examples, much 

 wider than those in similar spicules of recent .sponges. These 

 spicules are abundant and very uniform in size. The average 

 length of the arm of a fair sized spicule is 1,035 mm. and 

 its thickness near the centre is 0,09 nmi. The vertical arm 

 has a length of 0,2 mm. 



In the smaller form of quadrifid spicule (fig. 25) the four 

 arms are nearly equal in length and they are dispcsed so as 

 to form a more elevated pyramid. The average length ot 

 each arm is 0,45 mm. and the thickness near the centre 

 0,045 Tim. These spicules are also very abundant. 



From comparisons which I have made with specimens of 

 Pachastrella aniygdaloidcs . Carter , and P. geodioides . Carter 

 (An. Alag. Nat. Hist., S. 4, Vol. 18, p. 406, PI. XIV, figs. 22, 

 23) from the Atlantic, I find that there is a striking resem- 



