26 ART. 9. 1. I.TIMA I HEXACTINELLIDA. 



considerably over one millimeter in length and 40 }>■ thick near 

 the base but slightly thicker farther outwards. The outer end of 

 the ray is tapering, but the extreme tip is found invariably 

 broken off. Except at the basal portion and also to a certain 

 extent at the outer end, the ray is furnished with low, conical 

 and irregularly distributed tubercles, which are however never 

 very numerous. The apices of the tubercles, not always pointed 

 but often rounded, are directed either laterally or obliquely out- 

 wards. — A spicule exactly like the marginalia here described was 

 also discovered in the preparations of Specimen B, which, by 

 macroscopic observation, showed no trace of a marginal palisade. 



The sieve-plate beams are composed mainly of the paren- 

 chymal diactins, which are here somewhat shorter than in the 

 lateral wall. Certain hexactins situated in the midst of these 

 diactins are certainly to be considered as likewise parenchymal ; 

 but other hexactins and pentactins of regular shape and occuring 

 superficially in some numbers undoubtedly represent the dermalia 

 — and perhaps also the gastralia — in this region of the body. 

 The said hexactins and pentactins have an axial length of 2G0 p 

 on an average ; the tapering rays vary in thickness at the base 

 from 4 /* to 15 /a Among these spicules I have sometimes ob- 

 served, more frequently in Specimen B than in Specimen A, 

 abnormalities in the form of distorted rays, of tubercular formations 

 or of amalgamated parts of other spicules. The irregular looking 

 spicule given by W. Thomson ('68) in his fig. 1 a undoubtedly 

 comes under this head. 



From both Specimens A and B I have a parietal osculum 

 cut out and made into preparations. In these I do not find any 

 specially differentiated oscularia. 



I now come to consider the peculiar spiny microhexactin 



