214 Dublin Microscopical Club. 



form Euastrum Annstronginnum, a species not yet detected out of 

 Connemara. It occurs in deep and limpid water, the ponds being 

 such as are kept constantly at a maximum degree of fulness from a 

 bottom " spring." This is not a very pretty, but exceedingly well- 

 marked and distinct form. 



Histology of Foot of Solen. — Mr. P. S. Abraham, F.R.C.S., M.A., 

 B.Sc, showed, under a low power, transverse and longitudinal sec- 

 tions, taken near the apex of the foot of Solen, with a view to 

 demonstrate the arrangement of the muscular tissue of that organ. 

 The unstriped muscle-fibres are arranged in layers and bundles 

 which have broadly the following distribution : — Beneath the sub- 

 epidermic loose tissue is a layer of transverse or circular fibres, which 

 are particularly well marked at the sides of the foot. Then cornea 

 a thick layer of longitudinal bundles, somewhat differentiated into 

 two layers in the ventral half of the section, and everywhere 

 traversed by radial cross bundles and connective-tissue septa. 

 Next follows a thick transverse layer, which gradually thins out 

 towards the sides and becomes lost in the dorsal part of the section. 

 The deeper parts of the section are seen to be made up chiefly of 

 longitudinal bundles, freely crossed by thinner transverse and diago- 

 nal layers and bundles. Interspaces freely communicating together 

 and with a central larger one are abundant throughout the 

 sections. 



November 17, 1881. 

 Nostoc Zetterstedtii, J. E. Aresch.,/rom the Malar Lake. — Dr. E, P. 



stedt in the Malar Lake ; it was first described by M. Areschoug in the 

 Algae Exsiecatse of Wittrock and Nordstedt, 1872. It is distinguished 

 from all the other species of the genus, writes Bornet, " by its globu- 

 lous fronds aud its warty surface, composed of a number of more or 

 less deeply divided lobes, radiating from a centre to a periphery. 

 With age the frond would seem to become hollow in the middle ; its 

 consistency is firm and resisting ; its colour black when dry, of an 

 olive-green in fresh-gathered specimens ; the cells are subglobose or 

 oblong, a little contracted at the points ; the sheaths are indistinct, 

 and the gelatinous mass appears to be homogeneous in the central por- 

 tion of the frond ; at the periphery the sheaths are visible, and are 

 coloured of a slate-blue by the chloro-iodide of zinc. The heterocysts 

 are somewhat spherical, solitary or in groups of from three to twelve 

 attached in rows. Bornet regards as heterocysts and not as spores 

 those large cells attaining a diameter of 10 to 15 thousands of a milli- 

 metre, which form moniliform series intercalated in the trichomes ; 



thinks 



with 



internal wall which is coloured 

 ne> uncoloured : and in all the 



Nostoc 





never coloured by this reagent." In the very interior of each mass 

 Dr. Wright found a mass of lichen-like* tissue. 



