98 I. IJIMA : HEXACIINELLIDA. I. 



ness near the center. They are smooth all over but usually 

 show a gentle annular swelling at the center. They are not to 

 to be confounded with the rhaphides (PL V, fig. 30) which are 

 similarly grouped around the distal rays of dermalia but are of 

 a quite different origin and character. 



The oscularia (PI. IV, fig. 27) are of quite varied shapes 

 and sizes. The more common forms are diactins (corapass-needle- 

 like, with either two oppositely or four cruciately disposed central 

 knobs), thelactins, stauractins, paratetractins and pentactins. 

 Rays smooth, moderately thick, reaching 330," or more in 

 length and 35/' in thickness near the center. It is difficult to 

 point out which of the above mentioned forms is the predominant. 

 The diactins are more commonly located near the edge of the 

 oscular membrane ; some of the thetactin and pentactin forms 

 stand intermediate respectively to the parenchymalia and the 

 gastralia in points of general appearance and mode of occurrence. 

 For diftereuces from the oscularia of 7?. imperialis and B. oweni, 

 compare fig. 17, PL IF, with fig. 10, PL VI. 



The basalia (PL IV, fig. 26) have a broadly miter-shaped 

 anchor-head, measuring 90-110// across from tip to tip of the 

 oppositely standing teeth. The latter are strongly developed and 

 are 5 or 6, sometimes 7, in number. The apex of the head is 

 either rounded or pointed as in a Gothic arch. The shaft is 

 about 26/^ thick at the point of its origin fi'om tlie head, 

 whence it gradually narrows above until at a short distance above 

 the position of the axial cross (which lies nearly 1-50/^ away 

 from the origin of the shaft), the thickness measures not more 

 than 12//. It then begins to thicken again, up to the maximum 



