﻿EHRENBERG ON INFUSORIA IN GYPSUM. 



33 



similar to these two groups of Sepia-plates [Schulpen] are the two 

 groups of Aptychus. In the living Nautilus, the outer circum- 

 ference of the shell corresponds with the abdominal side of the ani- 

 mal, but its inner wall, lying close upon the former whorls, and pro- 

 tected by them, corresponds with the back of the animal. Such also 

 was doubtlessly the case with the Ammonites, whose ventral side, not 

 being protected, was exposed to injury when the animal protruded 

 itself from out of its chamber. On this ventral side were the bran- 

 chise, directly beneath the mantle. If the mantle were torn, the 

 gills were exposed, and not only was the respiration endangered, but 

 the animal's power of motion was also interfered with, because, as the 

 Ammonites swam by the forcing out of the water used in respira- 

 tion, the animal with a torn branchial sac was no longer able to direct 

 this stream in a certain direction, but was obliged to allow it to flow 

 off in all directions. If, then, we suppose these Aptychits-sheWs, which 

 were capable of falling or clapping together, were lying in the abdo- 

 minal portion of the mantle over the gills, then the latter were pro- 

 tected. The motion of the mantle, by its opening and shutting 

 during the act of respiration, did not only allow, but even enabled 

 the Aptychus to open and to close itself again ; nor was there any 

 hindrance to the animal's withdrawing itself into its shell. If the 

 soft parts of the Ammonite at death fell out of the shell, the Apty- 

 chus also fell out with it. Each species of Ammonite must conse- 

 quently have had its peculiar Aptychus. 



As there exists also a third group of naked Cephalopods that are 

 destitute of internal plates ; so there might possibly have existed a 

 third group of Ammonece without these internal bodies ; a circum- 

 stance, perhaps, explanatory of the fact of our finding so many Am- 

 monites in which no trace of Aptychus is present. 



[T. R. J.] 



On a Gypsum Bed containing Infusoria. By Prof. Ehrenberg. 



[Monats-Bericht Akad. Wiss. Berlin, 1849, p. 193-195 ; and Leonhard u. 

 Bronn's N. Jahrb. f. Min. 1850, 4 H. p. 491.] 



Infusoria have not hitherto been discovered in gypsum. A speci- 

 men of white gypsum, — brought by H. v. Tschichatschef, of Peters- 

 burg, from the country between Kepene and Hamsi-Hadje, in Phry- 

 gia, — formed of lenticular, densely crowded crystals, l"'-3"' in size, 

 which are imbedded in a white cement of a loose texture and effer- 

 vescing with acids, — was found to contain a very great proportion of 

 particularly large and beautiful siliceous Infusoria. The geological 

 relations of this rock will be detailed in the account of H. v. Tschi- 

 chatschef s Travels. Microscopic analysis gives 45 determinable 

 forms ; of which 38 are Polyyastrica, 6 Phytolitharia, and 1 Ento- 

 mostracon (fragment of valve). From the perfect absence of true 

 marine species, the presence of the siliceous parts of phanerogamic 

 land-plants, and the occurrence of Pinnularia Rhenana, characteristic 

 of the Brown-coal-formation near Rott in the Siebengebirge, the au- 

 thor considers that this gypsum is of freshwater origin, and probably 



VOL. VII. — PART II. D 



