402 On the Microscopic animals of the North Sea. 



species with 6, 7, 8, 9, 10, 11, 12, and 15 rays, and which are 

 designated Actinocyclus biternarius (with the senarms, which is 

 also found), A. septenarius, A. octonarius, A. nonarius, A. den- 

 arius, A. undenarius, A. bisenarius (not duodetiarius), and A. 

 quindenarius. Of the whole of this subdivision, there were 

 no living forms previously known, so that the members of it 

 were supposed to characterize the chalk-marl of the ancient 

 world, which is, therefore, now disproved. All these forms 

 are polygastric infusoria of the family Bacillaria. 



M. Ehrenberg has likewise found in a living state, in the 

 water near Cuxhaven, which he examined with care about a 

 year ago, three calcareous Polythalamias of the chalk, and 

 two siliceous infusory animals of the chalk-marl. These are 

 Fotalia globulosa, F. perforata, Textilaria globulosa, Gallionella 

 sidcata, and Navicula didymus. 



To these seventeen forms of the present world, and of the 

 chalk-formation, are to be added two other siliceous infusory 

 which occur alive in the seas of the North, and which have 

 lately been detected in the chalk-marl, viz., Striatella arcuata, 

 and Tesella catena. 



The above nineteen forms of the chalk, and which are new 

 as recent ones, together with those announced in October 1830 

 and June 1840, make the number of genera of these animal- 

 cules twenty-one, and of species forty, partly polythalamias and 

 partly infusory animals, which are common to the present 

 world and the chalk-formation. Anatomical preparations or 

 drawings of all these forms were submitted to the Academy. 



Notice regarding a cheap and easily used Camera Lucida, ap- 

 plicable to the delineation of Flowers and other small objects. 

 By Sir John Robison, K. H., F.R.S.E., M.S.A. Commu- 

 nicated by the Society of Arts for Scotland.* 



March 13. 1841. 

 Dear Sir, — In compliance with the wish expressed at the 

 late meeting of the Society of Arts, I beg to send you a de- 

 scription and sketch of the Camera Lucida which I then exhi- 

 bited. I again repeat, that its applicability to the delineation 

 of objects is confined to such as are of small size, and as may 

 be laid beside it on the drawing board. It is in this way par- 



* Exhibited to the Society of Arts, 8th March 1841. 



