CAULOPHACUS SCHULZEI. 



59 



have seen two branches arising at different points and extending in nearly the 

 same direction. 



Wilson {loc. cit.) does not mention such spicules as occurring in the specimens 

 examined by him. 



In the rare transitional (adolescent) forms described above, connecting the 

 oxyhexasters, etc., with the fully developed discohexasters, etc., the rays and 

 branches are quite smooth along their length but crowned at the end by small 

 verticils of recurved spines. By an increase in the thickness of all parts, by a 

 growth of the terminal spines, and by the addition of lateral spines along the 

 length of the rays and branches, these adolescent forms become adult discohex- 

 asters, etc. 



The adult discohexasters, hemidiscohexasters, and discohexactines (Plate 8, 

 figs. 10, 11; Plate 9, figs. 1-7, 9-13, 17-26; Plate 10, figs. 27a, 28a, 29a) have, 

 including the branches, six to seventeen rays and measure 139-264 fi in total 

 diameter. In the large specimens D and E these spicules attain a larger size 

 (diameter of largest 264 and 260 /j respectively) than in the smaller specimens B 

 and C, where the largest measured were only 240 fi in diameter. The basal 

 thickness of the rays is 6-15 m- The total diameter, and to a certain extent also 

 the basal thickness, of the rays are, as the subjoined table shows, in inverse 

 proportion to the number of rays (branches) . 



DISCOHEXASTERS, HEMIDISCOHEXASTERS, AND DISCOHEXACTINES.' 



In the large specimens D and E the discohexactines with six simple un- 

 branched rays are the most frequent. In the small specimens B and C on the 

 other hand the majority of these spicules are hemidiscohexasters and disco- 

 hexasters with branches on one to all six rays. 



' This table is based on the measurements of the discohexasters, etc., of all the specimens examined. 



