BY E. P. HALLMAXN. 789 



(ii.) The auxiliary or dermal styli (Text-fig. 3, b) are smooth, 

 almost invariably quite straight, and (like the principal styli) 

 somewhat abruptly sharp-pointed; and are frequently provided 

 with a minute muero on the basal extremity (Text-fig. 3, c) . 

 They range from 155 to 250/a in length and from 3.5 to 7/i.in 

 diameter. 



Microscleres. — The only microscleres (Text-fig. 3, d) are mod- 

 erately scarce, extremely slender chelae of the palmate type, 

 measuring from 11 to 15.5|u,in length, and peculiar in the fact 

 that the flukes at one extremity (more especially the median 

 fluke) usually exhibit some degree of atrophy — occasionally 

 being reduced almost to the verge of disappearance — and fre- 

 quently are disposed asymmetrically relatively to those at tne 

 opposite extremity, by rotation about the shaft amounting some- 

 times to as much as 90°. The flukes are relatively small — even 

 the median one seldom exceeding 4/x, in length. 



hoc— Coast of New South Wales, in and near Port Jackson. 



Genus Isopenectya, gen. nov. 



Definition. — Desmacidonidae without microscleres, in which 

 the skeleton is a renieroid reticulation either regularly isodictyal 

 throughout and composed entirely of spongin-ensheathed acan- 

 thostyli of a single kind, or also sparsely traversed by pauci- 

 serial spiculo-spongin fibres containing, in addition, smooth styli 

 of a form that suggests their original derivation from the acan- 

 thostyli ; in either case the acanthostyli are replaced in the outer- 

 most region of the skeleton by the smooth styli, which project 

 from the surface of the sponge. Also present are megascleres 

 of a third kind, in the form of smooth slender styli, occurring 

 dermally and interstitially. Typically the amount of spongin in 

 the skeleton is comparatively small. 



Type, I. chartacea Whitelegge (24); the only species. 



In the absence of microscleres the affinities of this genus are 

 somewhat uncertain. In certain respects, including the pattern 

 of the skeleton, it shows some degree of resemblance to Subero- 

 telites demonstrans Topsent (21), but in the latter species the 

 acanthoscleres are tylostrongyla, and auxiliary megascleres are 

 wanting. The existence of species like those of Suberotelites 

 suggests that the correct position of the genus Metschnikoivia 

 Grimm, — placed by Lundbeek in proximity to Reniera, — is like- 

 wise in the family Desmacidonidae. 



