STAUROCALYPTUÖ PLEORHAPHIDES. 229 



as gastralia there occur only diactins though in somewhat 

 diminished numbers. 



The oxyJiexasiers (PL XYI., lig. 7), occurring in moderate 

 abundance in all parts, are partly normally developed and partly 

 hemihexactinose. Hexactinose forms, with the terminals either 

 straight throughout or bent at base, were met with in only a few 

 cases. Diameter, 114/^ on an average. The terminals are rather 

 strong, measuring about 2 u. across at base ; they are nearly straight 

 or slightly bent and show a rough surface, due to microtubercles 

 which are sometimes distinctly retroverted but never much pro- 

 longed. The principals are extremely short and often almost 

 obsolete. 



In most normal oxyhexasters all the principals bear two 

 terminals each, so that the total number of terminal points is 

 tw'elve. Sometimes some — not all — of the six principals may show" 

 three terminals, in which cases the points in one spicule number 

 more than twelve in all. Thus, not larely have I come across 

 normal oxyhexasters with sixteen or seventeen terminal points. 

 In the hemihexactinose forms, the uniterminal rays are either 

 straight or bent at base, the rest of the rays being always 

 biterminal. 



The peculiarly twisted and evidently malformed oxyhexaster, 

 shown in PI. XVI., fig. 8, was observed l)ut once. It possesses 

 six terminals in all, but these evidently belonged not to as many 

 principals, but to the four or five remaining of the original six 

 principals. The curvature of the rays is in different planes, the 

 relative orientation of which could not be determined. 



The dUcociaders (PI. XVI., figs. 9-11) are present in abun- 



