58 CAULOPHACUS SCHULZEI. 



pinules. The dermal pinules of the upper part of the stalk are in all dimensions 

 smaller than the dermal pinules of the body of the same specimen. This differ- 

 ence is greatest in respect to the basal thickness of the distal ray. 



In the specimens examined by Wilson {loc. cit., p. 45) the proximal and lateral 

 pinule-rays measure about 100 by 8-10 /jl. These rays, particularly the laterals, 

 are, according to this, considerably smaller in Wilson's specimens than in those 

 examined by me. The distal pinule-ray is, according to Wilson (loc. cit., p. 45), 

 covered with narrow scales not over 16-20 fx long. His measurements agree 

 with mine, but it does not seem correct to call these structures scales. As my 

 photographs (Plate 11, figs. 15, 16) show, they are ordinary conic spines with a 

 fairly circular transverse section. Wilson {loc. cit., p. 46) gives sets of measure- 

 ments of the distal pinule-rays of two specimens, one in which they are slender 

 and one in which they are stout. The distal ray of the dermal pinules is (together 

 with its spines) in the first 240-320 /x by 36-40 n, in the second 210-240 ^ by 

 44-56 fi ; the distal ray of the gastral pinules in the first is 260-360 ju by 32-36 n, 

 in the second 280-320 a by 36-40 a. 



The oxyhexasters, hemioxyhexasters, and small oxyhexactines, found in small 

 numbers in several specimens, I at first took for skeletal elements sui generis. 

 A careful search, however, revealed the presence of a few spicules connecting them 

 with the discohexasters, hemidiscohexasters, and discohexactines, and the 

 examination of these transitional forms made it clear that these oxyhexasters, 

 etc., are young forms of the discohexasters, etc. 



The young oxyhexaster-like etc. of discohexasters etc. (Plate 9, figs. 14-16) 

 measure 60-190 n in total diameter, and have six rays. These are 2-4 ^ thick 

 at the base, conic, sharp-pointed, perfectly smooth, and either simple or provided 

 with one or two, rarely three, branch-rays. The spicules of this kind with all 

 six rays simple, which appear as small oxyhexactines, are very rare; in the 

 majority one or more (Plate 9, figs. 14, 15) or, less frequently, all rays (Plate 9, 

 fig. 16) bear branches. The simple rays are straight. Those bearing branches 

 diverge a little above the branching point shghtly in a direction opposite to 

 that in which the branch lies, but are straight apart from this divergence. The 

 branches arise at a distance of 12-20 fi from the centrum of the spicule, steeply, 

 sometimes nearly vertically, from the rays, but very soon curve sharply outward 

 and then again become fairly straight, remaining so to the end. Like the main- 

 rays themselves, these branches (branch-rays) are conic, sharp-pointed, and 

 perfectly smooth. When a ray bears more branches than one, they usually 

 arise at the same point and diverge in different directions. Exceptionally I 



