102 BATHYDORUS LAEVIS SPINOSISSIMUS. 



These four otherwise quite similar rays sometimes differ considerably in regard 

 to their spinulation. Thus the right lateral ray of the hexactine (Plate 15, 

 fig. 7) bears more numerous, larger, and more inclined spines than the left one. 

 The sixth ray, which lies in the continuation of the axis of the differentiated one 

 and which corresponds with the proximal ray of the true hexactine pinule, is 

 similar to the four (lateral) rays above described in size and spinulation, but is 

 slightly, sometimes considerably, curved (Plate 15, fig. 8). Also these rays are 

 on the whole stouter in the gastral hexactines of specimen A than in those of 

 specimen B. 



The oxyhexasters and (rare) hemioxyhexasters (Plate 14, figs. 16-32) measure 

 65-135 M in diameter. The main-rays are cylindrical, smooth, 4-12 yu long, and 

 2-4 M thick. They enclose angles of 90° with their neighbours. The main-rays 

 of the same spicule are equal. From the distal end of each main-ray a verticil 

 of from two to four end-rays, rarely only a single end-ray, arises. The main-rays 

 are often unequal in respect to the number of end-rays which they bear. A 

 single end-ray is found only on one or two of the main-rays of the spicule, the 

 others bearing more than one. The spicules with a single end-ray on one or two 

 of the main-rays, which must be designated as hemioxyhexasters, resemble the 

 true oxyhexasters in every respect except in regard to the end-ray number. 

 The end-rays arise very steeply from the main-rays but very soon curve outward, 

 that is towards the continuation of the main-ray axis, and then straighten out, 

 their distal and middle-parts being only slightly curved, or quite straight. The 

 angle between the chord of the end-ray and the continuation of the main-ray 

 axis is, on an average, about 45°. The end-rays are 30-60 ^ long and, at the 

 base, 1.6-2.5 /x thick, rarely as much as 3 yu. They are conic and taper gradually 

 to a very fine point. The end-rays are covered with rather sparse, backwardly 

 directed, slender spines, which decrease in size from the base to the tip of the 

 ray (Plate 14, figs. 24-32). The largest of these spines are 0.5-2 ^ long. 



The description given above shows that these sponges are most closely 

 allied to Bathydorus spinosus F. E. Schulze ^ and Bathydorus laevis F. E. Schulze 

 (Schulze and Ijima, loc. cit.) within which latter Wilson (Mem. M. C. Z., 1904, 

 30, p. 51, pi. 5, figs. 11-13; pi. 6, figs. 1-2) has distinguished the subspecies B. I. 

 spinosus. According to F. E. Schulze {loc. cit., 1897, p. 535) B. laevis and B. 

 spinosus are very similar and may be specifically identical. Judging from 



1 F. E. Schulze. Rept. Voy. ChaUenger, 1887, 21, p. 153, pi. 50, figs. 0-9. Sitzungsb. Akad. Berlin, 

 1897, p. 534. /. Ijima. Annot. zool. Jap., 1898, 2, p. 46. E. Topsent. Res. Voy. Belgica, 1901, 

 p. 36, taf. 1, fig. 1. 



