GEODIA LOPHOTRIAENA. 



183 



pointed at the cladomal end (Plate 47, fig. 17), 0.6-1.2 mm. long and, at the 

 cladome, 25-35 fi thick. In some the rhabdome is greatly reduced in length, 

 cylindrical, and terminally rounded. A spicule of this kind (Plate 47, fig. 21) 

 has a rhabdome only 0.2 mm. in length. The clades are usually fairly equal, 

 conical, pointed, curved, concave to the rhabdome throughout their entire 

 length, and 140-195 /t long. Rarely one clade is reduced in length and termi- 

 nally rounded. The cladome has a breadth of 240 370 /(. The chords of the 

 clades enclose angles of 102-114°, on an average 107.4°, with the axis of the 

 rhabdome. 



The dichotriaenes and the other lophotriaenes (Plate 47, figs. 9-16, 18-20, 

 25-33) usually have a simple, fairly straight rhabdome the cladomal half of 

 which is nearly cylindrical, the acladomal half conical and sharp pointed. Just 

 below the cladome the rhabdome is often slightly constricted. Very rarely a 

 downwardly directed branch-ray arises from the central part of the rhabdome 

 (Plate 47, fig. 20). The rhabdome is 0.8-1.2 mm. long and, at the cladome, 

 35-59 ft thick. The three main clades of the same cladome are usually equal, 

 straight, cylindrical, and 70-140 // long. They enclose, with the rhabdome, 

 angles of 105-130°, on an average 120.8°. The end clades are conical and blunt 

 pointed. When, as is the case in the dichotriaenes, there are only two end 

 clades on one main clade, the end clades are curved more or less, concave towards 

 each other (Plate 47, figs. 25-29). When, as is the case in the other lophotriaenes, 

 there are more than two end clades on one main clade, one end clade, or rarely 

 two (Plate 47, fig. 31) are straight and appear as continuations of the main clade, 

 the other end clades being curved more or less, concave towards these (Plate 47, 

 figs. 30-33). The end clades of the same cladome are usually unequal. The 

 true dichotriaenes are much more numerous than the other lophotriaenes. In 

 the latter one (Plate 47, figs. 30, 33), two (Plate 47, fig. 31), or, more rarely, all 

 three (Plate 47, fig. 32) main clades bear from three to five, instead of only two, 

 end clades. In the most regular dichotriaenes the end clades extend in a plane 

 nearly vertical to the rhabdome or are directed obliquely upwards (Plate 47, 

 figs. 9, 10, 13, 18). In other dichotriaenes and in most of the other lopho- 

 triaenes not all of the end clades are in this position, some being directed 

 downward (Plate 47, figs. 11, 12, 14, 19, 20). The length of the end clades is 

 70-180 //, the breadth of the whole cladome 300-500 /t. The axial threads of 

 the end clades of the dichotriaenes arise nearly at right angles from the end of 

 the axial thread of the main clade and then bend outward to assume the direc- 

 tion of the end clade. 



