GEODIA MEDIA. 199 



Derivates of styles, angularly bent in such a manner, are also met with 

 (Plate 16, fig. 13g). Occasionally amphioxes angularly bent at two places 

 have been observed (Plate 16, fig. 9w). In the simplest forms of the branched 

 amphiox- and style-derivates a small straight branch is observed arising near one 

 end of the spicule. This branch is generally directed upwards and encloses, 

 with the epirhabd-like continuation of the shaft of the spicule, a smaller (Plate 16, 

 figs. lOd, 13h) or a larger (Plate 16, fig. lOx) angle. Rarely it is directed down- 

 wards (backwards) (Plate 16, fig. llh). Generally there is only one branch, 

 but spicules with a cluster of two or more branches have also been observed 

 (Plate 16, fig. 13i). Some of these derivates are both branched and angularly 

 bent. Such forms have been found among the style-derivates (Plate 16, fig. 13k) 

 as well as among the amphiox-derivates (Plate 16, fig. 2j). Occasionally I have 

 observed spicules thickened and rounded at both ends which can be considered 

 as amphityle derivates of amphioxes or styles. These spicules have not been 

 mentioned by Bowerbank and Sollas, and in the former's tyjje they are indeed 

 very scarce. 



The small dermal styles (Plate 17, figs. 21b, 22d) are straight or slightly 

 curved and taper towards the distal pointed, and also towards the proximal 

 rounded end. The transverse diameter of the rounded end is a little more than 

 half the transverse diameter of the thickest central part, the average ratio be- 

 tween these two dimensions being about 10 : 6. In the digitate form these 

 styles are 140-190 ;i, usually 180-190 /i long and 2-5 fi, usually about 4 /£ thick. 

 In the massive form they are slightly larger, 150-265 /t long and 3-6 /( thick. 

 These spicules are not mentioned either by Bowerbank or by Sollas, but they 

 are very abundant in the former's type, and there measure 150-200 by 2-4 fi. 



Among the plagiotriaenes, as among the amphioxes, two forms, a slender and 

 a stout one, can be distinguished. As the intermechate forms connecting these 

 are not numerous and as the slender plagiotriaenes have longer clades than 

 most of the stout ones, showing that the former cannot be young forms of the 

 latter, I consider them as two distinct kinds of spicules. Both these types of 

 plagiotriaenes have been found also in Bowerbank's type. 



The slender plagiotriaenes (Plate 16, figs. Iq, 5r, 12q, 14q), are met with 

 in both forms but are not very numerous in either. Their rhabdome is straight 

 or slightly curved, conic, pointed, 1-1.6 mm. long and 17-30 n thick at the 

 cladomal end. The clades are generally considerably curved, concave to the 

 rhabdome, particularly in their distal part, and 160-260 fi long. The chords 

 of the clades enclose angles of 107-114° with the axis of the rhabdome. Similar 

 slender triaenes were also found by me in Bowerbank's type. 



