30 



SIDOXOPS ANGULATA. 



good deal longer than those of the plagio- and ortho-triaenes of the other two 

 varieties. The clades of the same cladome are equal (Plate 13, figs. 9,11,15,18), 

 or slightly (Plate 13, figs. 5, 6, 8, 10, 13, 14, 19) or considerably (Plate 13, figs. 

 7, 12, Hi) unequal in length. Generally the clades extend in a longitudinal plane 

 passing through the axis of the rhabdome; sometimes, however, (Plate 13, fig. 4) 

 an angular bend in a transverse plane is observed. Short clades are often 

 (Plate 13, fig. 7, 12), long ones rarely (Plate 13, figs. 9, 12), nearly straight. 

 Cienerally the clades are markedly curveil, conca^^e to the rhabdome. This 

 curvature increases towards the ends of the clades. In some (Plate 13, figs. 3, 

 13-16, 19) the degree of this increment of curvature is slight, in othei-s (Plate 13, 

 figs. 5-8) it is considerable. Sometimes the distal part of the dade is bent down 

 abruptly (angularly) (Plate 13, figs. 5, 10). The angles enclosed between the 

 dade-chords and the axis of the rhabdome are in the two specimens of var. 

 ^ megana on an average 101.3 and 103°, in var. mia-oana 105.6°, and in var. 

 orlholriaena 93.7°. These spicules are accortlingly in the first two plagio- 

 triaenes, in the last orthotriaencs. The clade-angles of the three clades of the 

 same rhabdome are usually about equal, rarely (Plate 13, fig. 6) considerably 

 different. 



Very rarely one of the clades becomes quite nidimentary. Such iliaene 

 spicules were found only in var. orthotriaena. 



DIMEX.SIOXS OF NORMAL PL.\GIO- AND ORTHOTRI.\ENE.S OF SIDONOPS ANGULATA. 



The rhabdomes of the anadades (Plate 12, figs. 1-15; Plate 13, fig. 17c) 

 are for a great part of their length nearly cylindrical. Of the long ones none 

 were found intact in the spicule-preparations, all being broken. The longest 

 fragment measured wa.s 9 mm., the longest rhabdome observed intact was 6 mm. 

 in length. The rhabdomes of the anaclades of var. microana appear to be 



