PORIFERA. II. 115 



Spicula: a. Megasclera are styli of two forms, larger ones forming- the skeleton, and smaller ones 

 forming the dermal reticulation. The skeletal styli are more or less curved, often a little irregularly, the 

 curve is generally found nearest to the rounded end; the opposite end tapers to a point of middle length the 

 outer end of which may be a little shorter pointed. The upper end of the styli is either quite smooth, 

 or the}' have, on the very uppermost surface only, a few exceedingly small spines appearing as a slight 

 creuulation. The length varies from 0-53 — o-8 mm , and the thickness is 0-013 — o-020 mm ; the longest ones are 

 far from being always the thickest ones; finer developmental forms occur, but in small numbers. The 

 dermal styli are straight, the head-end is often quite slightly swollen, so that they approach subtylostyli, 

 but they cannot, however, be designated as such; the opposite end tapers more or less, but always rather 

 little, and therefore the point is short. The most particular fact about them is that the head-end is gener- 

 ally or always slightly spined; some difference may be found in the spinosity, but it is only the very 

 uppermost part that is provided with more or fewer slight spines. The length of these needles is 

 between 0-29 and 0-39™'", the thickness is 0-005 — o - oo8 mm ; the shortest ones are often the thickest 

 ones. b. Microsclera. These are of two forms, isochelse palmatce and toxa. 1. The isochelse are of 

 a quite similar form as those of the preceding species; the shaft is quite slightly curved, the 

 middle part, making about one third, is straight, the tooth is a little narrower but of the same length 

 as the alse, the tuberculum is rather long and most distinctly conspicuous in its lower end. The length 

 of the chela is 0-014 — o-oi8 mm , and the breadth about ooo4 mm . 2. Toxa; the largest of the bows have 

 a similar form as in the preceding species, only the spinosity is, perhaps, a little finer, and it reaches 

 a little farther up the legs, and the outer part of the legs is generally not straight. The bows have 

 a length of up to o\40 mm with a thickness of o-oo4 mm . Of the bows thinner forms with slighter spinosity 

 mav be found, but I have seen no younger developmental forms. There is almost no variation in the 

 form of these bows. On the other hand smaller and finer bows occur in rather large numbers; some 

 of them are of a similar form, but the greater part have a considerably flatter curve; and rather fre- 

 quently a form is seen having a rather strong bend in the middle, but a little way from the bend 

 their legs turn horizontally and become straight or almost straight. The length of these bows was 

 measured to 0-085 — o-28 mm , and the thickness is in proportion from exceedingly fine, ca. o-ooo7 ,nm , to 

 o-0O2 mm . None of all these bows are spined; to judge from their form, they do not appear to be devel- 

 opmental forms of the bows before mentioned; the largest of them, which are of a similar form as 

 the preceding ones, may, however, be developmental forms of these. All the bows are frequently some- 

 what twisted. 



Of the bows a few specimens were seen of a quite colossal size, viz. 0"56 mm long, and o-oi4 mm 

 thick. These bows had no spines or only a few quite rudimentary ones. The question is here evidently 

 of monstrous forms arisen by a continued, abnormal silicious deposition, and by this continued depo- 

 sition the thorns have by and by become effaced. The same feature may be found in other forms; 

 thus in Clador/ifza-species I have found abnormal silicious deposition in the ancorse, so that they 

 became exceedingly thick, and the teeth were partly or almost entirely effaced. 



Of the microsclera the chelae occur very abundantly both in the dermal membrane and in the 

 body itself; the bows are not numerous, and were not seen in the dermal membrane. 



Remarks: On account of the localities from which Ridley and Dendy and I have the species, 



15* 



