100 



ART. 7.— I. IJIMA : HEXCTINELLIDA, IV. 



Text- figure 5. 



All oxyliexaster in tlie last stage 

 of becoming liexaetiiwse. 440 X . 



cases were incidentally met with more 

 than once in the present species. The 

 accompanying text- figure 5 sliow^s one 

 of them. Five of the rays are simple, 

 heing either straight or bent at base, 

 exactly like those in hexastinose forms 

 of the oxyhexaster ; in them the 

 principals are strictly uniterminal. 

 The sixth of the principals, which 

 are all of quite an obsolete length, 

 bears, Ijesides a normally developed 

 terminal, another of spurious size. 

 Were this as much developed as its fellow on the same 

 principal, we should have a normally hemihexactinose form in 

 which a single principal is biterminal and all the other five are 

 uniterminal. On the other hand, if it should altogether dis- 

 appear, as it apparently is on the verge of doing, the result 

 w^ould be a hexactinose form, the exact like of which may not 

 be difiicult to find among the oxyhexasters of the species. In 

 my experience certain other Rossellids have also yielded similar 

 cases of oxyhexasters being in the last stage of transition into 

 the hexactinose statu. 



HYALASCUS GIGANTEUS Li. 



PL VIII., figs. 3-16. 



Hyalaacus (j'lganteus, Ijima, *g8, p. 'jO, 



This species is described on the basis of a large fragment 

 which originally belonged to Mr. Alan Owston (O. C. Ko. 



