198 GEODIA MEDIA. 



silu in the scftioiis, have been observed in the spicule-preparations. One of 

 these, an anatriacne, its, in all probability, proper to the sponge. 



Among tlie large choanosomal amphioxes, two forms, a slender and a stout 

 one, can be distinguished. These are, it is true, connected by transitions, but as 

 the latter arc not at all numerous and as the slender amphioxes are longer than 

 most of the stout ones, and therefore cannot be considered as j^oung forms of the 

 latter, I am inclined to consider the slender and the stout amphioxes as distinct 

 forms. 



The slender, choanosomal amphioxes (Plate 16, figs. 3-5a) are quite frequent 

 in the digitate form but rare in the massive form. They are slightly curved, 

 fairly isoactine, not very sharp pointed, 1.3-1.5 mm. long, and 23-30 /i thick. 



The stout choanosomal amphioxes (Plate 16, figs. l-5b, 6z, 8b, z, llz) are 



very numerous in both forms. They are slightly curved, fairly isoactine, and 



gradually attenuated to the not very sharp-pointed ends. In the digitate form 



they are 1.2-1.55 mm. long and 33-51 n thick, in the massive form 1.3-1.7 mm. 



long and 35-51 [i thick. 



In Bowerbank's type, reexamined by me, I found choanosomal ampliioxes 

 1-1.0 mm. by 18-50 p.. Sollas gives their dimensions as 1.51 mm. b}^ 32 p. 



The large choanosomal styles (Plate 16, figs, llf, 13f) are not numerous. 

 Thej' are relatively more frequent in the massive than in the digitate form. 

 These styles are 0.9-1.3 mm. long and 30-50 p tliick. Some are for the greater 

 part of their length cylindrical, and simply rounded off at one end, othere some- 

 what attenuated towards, others again slightly tliickened at, the rounded end. 

 In four styles of the massive form the thickness was: — 



In the centre 36 n. at the rounded end 24 /( 



40 " " " " " 43 " 



" " " 43 ' ' 50 " 



" " " 50 " " " " " 40 " 



These spicules are not mentioned by Sollas; I found a good many, however, 

 in Bowerbank's tji^e. 



Both the digitate and the massive forms are exceedingly rich in irregular, 

 angularly bent or branched derivates of the amphioxes and styles described above. 

 In their dimensions these spicules agree with the regular forms from which they 

 are deri\-ed. The simplest form of amphiox-derivate is an amjjhiox very slightly 

 angularly bent near one end. This bend may be in the same direction as the 

 curvature of the spicule (Plate 16, fig. ly), or in a direction opposite to it (Plate 

 16, fig. 9y). In other amphiox-derivates of this kind the angular bend is much 

 more pronounced, the angle between its two limbs being smaller. Such a 

 spicule is represented on Plate 16, fig. 9c. 



