CORBITELLA AND HETEROTELLA. O 



The entire latticework-like wall is thin except at the region 

 of basal incrustations. The meshes which should have each con- 

 tained an osculum (both parietal and cribellar, cfr. Ijima, 'oi, 

 p. 39) are rather wide. The beams, filigree-like in structure, 

 are never more than 1 mm. thick. They combine to form a 

 latticework of an irregular kind (vide fig. in either Gray '67, 

 or Thomson '68). Many of the stronger beams are seen to 

 pursue a flexuous course, on the whole longitudinally directed ; 

 some others run, at least for a short distance, in a direction more 

 inclined to the transverse or the oblique. However, irregular 

 deviations in the course as well as in the branching and anasto- 

 mosing are of such frequent occurrence that it is scarcely possible 

 to distinguish separate systems of beams such as are seen in 

 Eupleciella. So far as the skeletal tube goes, there exists no 

 indication of parietal ledges. Although I have no observation 

 on the megascleric elements of the beams, it seems to me more 

 than probable that both the comitalia and principalia paren- 

 chymal are, at least mainly, diactins. 



Of the interstitial loose tissue, I have fortunately found some 

 vestiges still left, scantily attached here and there to the skeletal 

 framework. They had to be searched for by means of a lens. 

 By careful manipulation with pins or a pair of pincers, I suc- 

 ceeded in securing the tissue in a quantity sufficient to make of 

 it a number of microscopical preparations, an examination of 

 which revealed some points of great systematic importance to the 

 genus and the species. 



W. Thomson ('68, p. 131) communicated some information 

 respecting the loose spicules of this species, but it was so little 

 that not much use could be made of it for the systematic. And 

 moreover, soon after I had gone into the study of the Euplec- 



