178 GEO 01 A AMPHISTRONGYLA. 



actino fonxis of such, in whicli tlie thinner end has become attenuated to a fine 

 point. 



The plagiotriaenes (Plate 20, figs. 22, 25) have conical, usually rjuite straight 

 rhabdonies, 1.8-2.2 mm. long and 22-32 // thick at the cladomal end. The 

 acladomal end is usually simply rounded off and 3-10 /x thick, rarely slightly 

 thickened. The clades are slightly curved, concave to the rhabdome, conical, 

 usually regularly arranged, with angles of 120° between them, and, in the same 

 cladonie, of equal size and in nearly the same position to the rhalxlome. The 

 clades are 155-190 /« long and enclose angles of 103-120°, most frecjuently about 

 109°, with the rhabtlome. Rarely the clade-rhabdome angles of the same 

 rliabdome are vcrj' dissimilar. In one plagiotriaene-cladome of this kind one 

 of the three clades was nearly ujn-iglit, resemljjing in its jjosition an ejjirhabd. 

 This sword-like sjiicule might be termed a mesorthodiaene. 



Among these plagiotriaenes similar forms with reduced cladomes, which 

 ap])ear a.s plagiodiaenes or plagiomonaenes occur. The monaene forms are more 

 frequent than the diaene. The cladome of a normal monaene of this kind is 

 shown in Plate 20, fig. 23. Very rarely the rhabdome is reduced in length and 

 in that cii.se cylindrical and slightly thickened at the aclatlomal end. One of 

 tliese spicules (Plate 20, fig. 24) has a rhabdome, only 285 /i long, and a single, 

 bifurcate clade, arising at an angle of hardly more than 90° from the rhabd- 

 ome. This spicule is an orthodichomonaene. Dichoclade forms of this or 

 any other description are, however, exceedingly rare. 



Owing to the loss of nearly the whole of the spicule-fur I found but few 

 mesoproclades (Plate 20, figs. 7, 8), wliich presumablj^ form the greater part of 

 this fur. None of them had an intact rhabdome, so that I cannot give its length. 

 Most of the mesoproclades observed were triaene, but monaene forms (Plate 20, 

 fig. 7) have also been met with. The rhabdomes of these spicules are, at the 

 cladome, 3-5 pt thick; the epirhabds are straight, conical, sharp pointed, and 

 16-22 fi long; the clades are concave to the epirhabd, usually rather blunt, and 

 40-60 pL long. The dade-epirhabd angles of the intact cladomes observed 

 were 36-41°, but some broken mesoprotriaene cladomes seen indicate that 

 occasionally this angle is considerably larger. 



The anatriaenes (Plate 20, figs. 5, 6, 10, 11) are, like the mesoproclades, 

 scarce in the preparations, and probably for the same reason. Anatriaenes 

 with intact rhabdomes were not observed. Their rhabdomes are 1.5-4 [x thick 

 at the cladomal end, the clades are conical and sharp pointed, more (Plate 20, 

 figs. 5, 10) or less (Plate 20, figs. 6, 11) curved, concave to the rhabdome in their 



