on the Organic Composition of Chalk and Chalk Mark 389 



the discs are twice as thick as in Sorites. If we compare So- 

 rites with Fliistra^ we may place Amj)hisorus by the side of 

 Eschara^ but, being both free moving bodies, they are different 

 from them. 



Plate IV. contains the invisible animalcules of the chalk 

 and chalk marl, displayed in twelve specimens of rock ; 1 to 9 

 being portions from the chalk, and 10 to 12 from the chalk 

 marl, magnified 300 times. In these specimens the calcare- 

 ous Polythalamia amount to sixteen species, and the siliceous 

 Infusoria to twelve species, with siliceous spicula of sponges. 

 The twelve localities from which these specimens of the rock 

 masses were derived are the following: — 'No. I to 5, ivritiiig 

 chalk; namely, 1. from Puszkary, in Poland, opposite Grod- 

 no, from the shore of the Memel ; 2. from Jutland, in Den- 

 mark ; 3. from the island of Rligen in Pomerania; 4. from 

 Gravesend, on the Thames; 5. from Meudon, near Paris; 

 frmer writing chalk, No. 6, from Cattolica in Sicily; com- 

 ]}act, not "d-riting chalk. No. 7, from the Mokattum hills near 

 Cairo ; and No. 8, from the Catacombs of Thebes in Upper 

 Egypt; compact gray limestone, No. 9, from the mountain 

 mass of Hamam Faraun in Sinai, Arabia; chalk marl, No. 

 10, from Oran in Africa; No. 11, from Caltasinetta in Sicily; 

 No. 12, from Greece. 



In the general table indicated above, under the head of No. 

 13 of the contents of the memoir, a list is given of the princi- 

 pal forms of the invisible organic bodies which constitute 

 the rocks from which the twelve above-mentioned specimens 

 were taken, as well as the chalk of Brighton, the chalk marl 

 of Zante in the Ionian Islands, and the nummulite limestone 

 of the Pyramids of Geza in Egypt. From this it results that 

 the principal forms in these rocks consist of twenty-five spe- 

 cies of calcareous-shelled Polythalamia, thirty-nine species of 

 siliceous-shelled Infusoria, seven species of soft-shelled Infu- 

 soria of the flints, and five species of siliceous plants. 



The twenty-five species of calcareous-shelled Polythalamia, 

 belonging to eight genera, are the following: — 



Flustrella coyiccntrica; Globigerina btdloides?, G. helicina'^; 

 Planulina siada, P. *turgida; HobuVma C7et a cca', llosalina 

 ■foveolata, R. globidaris?, R. *lcevigata, H.pcrtnsa; Rotalia 

 *globulosa, 11. ocellata, R. ornata, R. perforata, R. scabra, 

 R. stigma ; Textularia acicidata ?, T. '*aspera, T. brevis, T. 

 *dilata/a, T. *globidosa, T. perforata, T. spinosa, T. * striata ; 

 Turbinulina italica? Quinqueloculina? from Benisuef, is 

 doubtful. N.B. Texttdaria globulosa, when in fragments, is 

 not easily distinguished from Rotalia globulosa ; and in like 

 manner the fragments of Textularia j^oforata may be con- 

 founded with Rotalia perforata. 



