ERYLUS SOLLASII. 



279. 



reduced, cylindrical ones 140-220 /< long. Their thickness at the acladonial 

 end is 8-22 p.. Cylindrical rhabdomes are always thick; all the slender triaene- 

 rhabdomes observed were conical. The triaenes of the small specimens (race I, 

 forms A and B) have somewhat shorter and very much thinner rhabdomes 

 than those of the larger ones. The averages of three thickest of the former 

 being 10-13, those of the latter 18-21 /i. Among the large specimens the one of 

 race III has far larger triaene-rhabdomes than those of the races I and II. 



The cladomes of these triaenes are very polymorphic. Triaenes with 

 simple clades occur in all the specimens. In race I, form A, no other triaenes 

 were observed. In race I, forms B, C, and in race II a few triaenes with one, 

 more rarely two or three branched (bifurcate) clades occur besides the ones 

 with simple clades. The ramification of the triaene-clades is still greater in 

 race I, form D, and in race III : in these the triaenes with branched clades are 

 more numerous than the ones with simple clades. 



In the triaenes with three simple clades (Plate l, figs. 7, 11, 12, 15-20, 

 24-26) the clades are usually conical and blunt pointed, rarely reduced in 

 length, cylindrical, and rounded at the end (Plate 1, figs. 16, 18). Such a reduc- 

 tion of the clades is usually associated with a reduction or other abnormity 

 of the rhabdome. The simple triaene-clades are slightly and uniformly curved, 

 concave to the rhabdome (Plate 1, figs. 17, 19), or nearly straight (Plate l, figs. 

 22, 25), or, more rarely, abruptly bent down at the end (Plate l, figs. 18, 20, 

 24). Their chords are 120-300 // long. 



As stated above, one, two, or all three clades of the triaenes may be 

 branched. This branching is most frequently a simple and regular bifurcation, 

 the two branches (end clades) being simple, and fairly equal in length and angu- 

 lar position (Plate l, figs. 6, 9, the lower ones in fig. 10; Plate 3, the lower left 

 ones in figs. 2, 3, 5, 6). Irregularities due to a difference in the length or the 

 position of the two branches or to secondary ramifications of the branches are 

 frequently met with. The difference in the length of two end clades forming 

 a pair is caused by the reduction of one of them. This reduction sometimes 

 becomes so great as to lead to a complete suppression of one of the end clades, 

 in which case a single end clade arises from the, in such spicules usually some- 

 what thickened end of the main clade (Plate 1, fig. 8). The differences of posi- 

 tion are frequently so great that one end clade appears as a continuation of the 

 main clade (Plate l, the upper one in fig. 5; Plate 3, the upper one in fig. 3). 

 Some of these spicule-rays might indeed be considered as simple clades from 

 which a branch-ray arises laterally. A secondary ramification of the end 



