158 



GEODIA BREVIANA. 



One of these rhabdomes possessed several irregular thickenings near the rounded 

 end, under which the axial thread passed smoothly without any thickening or 

 other modification. The clades are conical, pointed, and uniformly curved in 

 their entire length, concave to the rhabdome. The degree of the curvature 

 usually is, as in the two triaenes represented on Plate 35, figs. 15, 16, quite con- 

 siderable, rarely so slight as in the long (left) clade of the triaene (Fig. 17). 

 Occasionally triaenes with clades bent much more strongly than those represented 

 in Figs. 15 and 16 have been observed. The clades are nearly always simple; 

 very rarely one of them is bifurcate. The clades of the same cladome are usually 

 similar, irregular cladomes being exceptional. The chords of the clades are 280- 

 500 /< long and enclose angles of 94-108°, on an average 101.6°, with the axis of 

 the rhabdome. Of the seventeen triaenes the clade-angles of which were meas- 

 ured, four were orthotriaenes with clade-angles less than 100°, the other thirteen 

 plagiotriaenes, with clade-angles 100° or more. In the specimen described by 

 Lambe the plagio-orthotriaenes have rhabdomes 2.2-4.1 mm. (Lambe, 1893, 

 2.4 mm.) by 60-105 p., clades 340-680 [i (Lambe, 1893, 700 /i) long, and clade- 

 angles of 97-113°. 



The mesoprotriaenes (Plate 35, fig. 14) have a rhabdome about 15 p. thick at 

 the cladome, an epirhabd 105 a long and clades, curved concave to the epirhabd, 

 the chords of which are 115-130 p long and enclose angles of about 38° with 

 the epirhabd-axis. In the specimen described by Lambe the mesopro triaenes 

 have rhabdomes 7-11 mm. (Lambe, 1893, 7.84 mm.) by 15-32 p, clades 65-250 n 

 (Lambe, 1893, 95 fx) long, clade-angles of 20-44°, usually 32-44°, and an epirhabd 

 120-310 /( long. 



The large anatriaenes (Plate 35, figs. 5-7) have a nearly cylindrical rhabd- 

 ome, 25-40 p thick in its cladomal part. I found no intact rhabdomes of these 

 spicules; the fragments observed indicate that they attain a considerable length. 

 The clades are slightly and uniformly curved or somewhat angularly bent near 

 the end, concave to the rhabdome. They are remarkably thick at the base, 

 and usually simple and quite sharply pointed, but anatriaenes with one clade 

 bifurcate have also been observed occasionally. The two terminal branches of 

 such clades are nearly parallel and lie close together. The chords of the clades 

 are 60-115 p. long and enclose angles of 50-65°, on an average 57.3°, with the 

 axis of the rhabdome. In the specimen described by Lambe the large ana- 

 triaenes have a rhabdome 9-11 mm. (Lambe, 1893, 7.5 mm.) by 25-37 pt, stout 

 clades 47-82 p (Lambe, 1893, 60 p) long, and clade-angles of 52-63°. 



In the specimen described by Lambe a few anadiaenes similar to the ana- 



