DUBLIN MlCROSCOPtCAL CLUB. 425 



or augite, which are, in all probability, grains of olivine or pseudo- 

 mor|)hic after that mineral. The rock is largely crystalline, granular, 

 and has been called " anorthite-syanite ;" but, as the basic mineral is 

 augite rather then hornblend, and as silica is altogether absent, the 

 name already applied to it seems the most appropriate. 



Microscopical Structure of Spines of Gentrostephanus Rodgersii, 

 Agassiz. — Mr. H. "W. Mackintosh exhibited transverse sections of 

 spines of Centrostephanus Rodgersii, A. Agass. In this form the 

 spines, though agreeing in being hollow and deep crimson in colour, 

 differ considerably in external appearance and internal structure. 

 One set are fusiform and longitudinally costate, and, in section, 

 show the central cavity to be surrounded by a network of consider- 

 able extent, which sends out short prolongations to bound the 

 wedge-shaped solid pieces, whose external rounded projections form 

 the surface ridges, and which show a series of strise (like those on 

 starch-grains of potato) surrounding a more or less distinct point 

 situated near the base of the wedge ; the interspaces of the reticula- 

 tions are irregular, both in shape and disposition, except along the 

 line joining the bases of the solid pieces with the centre, where they 

 are tolerably uniformly quadrilateral, and placed directly behind one 

 another. The other form of spines tapers gradually from the base 

 to the point ; they are abruptly serrate, and have the central cavity 

 much wider ; they display in section a series of urn-shaped solid 

 pieces (with thin strise, much less distinct than in the wedges), 

 whose stems arise from a narrow ring surrounding the central space, 

 and are joined by an extremely irregular band of reticulations ; 

 the solid pieces are also united by broad solid bands irregularly 

 placed. 



Sporangium-like Structure in Polyactis. — Mr. Pirn showed a 

 seemingly peculiar condition of a form of Polyactis, presenting, 

 supported on branches of the hypha, what appeared to be fruit-like 

 or sporangium-like bodies of a globular figure, in which he believed 

 he had seen a division of the contents into a number of spores. The 

 present specimen had somewhat altered since being put up, and 

 these bodies now offered the appearance of globular mucous heads 

 to the supporting stipes, with a number of minute granules or 

 corpuscles within. 



Pentastomitm proboscideum, Diesing, exhibited. — Dr. A. Mac- 

 alister exhibited a specimen of Pentastomum from the lung and 

 peritoneal cavity of Poa imperator. The species is closely allied to, 

 if not identical with, Pentastomum proboscideum, Diesing, The 

 specimens found were all females, and showed eggs in different de-. 

 velopmental stages. He deferred any further account until he had 

 time to examine all his specimens, and to compare them with 

 another species of Pentastomum recently obtained by him from 

 Aonys. 



Cylindrocapsa involuta, Reinsch, new to Britain, exhibited. — 

 Mr. Archer showed an algal form, doubtless identical with Cylin- 

 d/rocapsa involuta, Reinsch (' Algenflora des mittleren Theiles von 

 Frauken,' p. 66, T. VI, f. 1, a, b, c), though that author's description 



