Tyrol are very rich, and have furnished about one-third of all the Radiolaria known from the Jura; most of the species too are very well preserved (compare § 243). Regarding the remarkable composition and manifold varieties of the Jurassic Radiolarian quartz, the very full treatise of Dr. Rüst may be consulted (L. N. 51). The very interesting Radiolarian coprolites, which that author has discovered in the lower and middle Jura of Hanover, occur in astonishing numbers in the iron mines at the village of Gross-Ilsede, four and a half miles south of the town of Peine. They constitute from 2 to 5 per cent. by weight of the Liassic iron ore; of this latter, in the year 1883 alone, not less than two hundred and eighty million kilograms were excavated. It is very probable that the careful microscopic examination of thin sections of coprolites, as well as of flints, chert, jasper, and other quartzites, would yield a rich harvest of fossil Radiolaria in other formations also. In Italy Dante Pantanelli has discovered interesting Polycystine jaspers in Tuscany (L. N. 36, 45); these also appear to occur in the Jura (compare § 243, and L. N. 51, pp. 3-10). 249. _Fossil Groups._--The preservation of Radiolaria in the fossil state is, of course, primarily dependent on the composition of their skeleton. Hence the ACANTHARIA, whose acanthin skeleton although firm is readily soluble, are never found fossil. The same is true of the skeletons of the PHÆODARIA, which consist of a silicate of carbon; here, however, a single exception is found in the Dictyochida, a subfamily of the Cannorrhaphida, the isolated parts of whose skeletons appear to consist of pure silica, and {clxxiv}are often found fossil. Of the two other legions those families which possess no skeleton are of course excluded; the Nassellida among the NASSELLARIA, and the Thalassicollida and Collozoida among the SPUMELLARIA. Thus of the 85 known families there remain scarcely 55 of which the skeletons may be expected in the fossil state; and of these scarcely half have been actually observed in this condition. Of the 20 orders of this class enumerated in § 155, the following 9 may be, for palæontological and geological purposes, completely excluded:--(A) The 4 orders of ACANTHARIA (1, #Actinelida#; 2, #Acanthonida#; 3, #Sphærophracta#; 4, #Prunophracta#); (B) 3 orders of PHÆODARIA (5, #Phæosphæria#; 6, #Phæogromia#; 7, #Phæoconchia#); (C) 1 order of NASSELLARIA (8, #Nassoidea#); (D) 1 order of SPUMELLARIA (9, #Colloidea#). From a geological point of view the following 6 orders, although occasionally found fossil, are of quite subordinate importance:--(A) Among the SPUMELLARIA (10, #Beloidea#, and 11, #Larcoidea#); (B) among the NASSELLARIA (12, #Plectoidea#; 13, #Stephoidea#; 14, #Botryodea#); (C) among the PHÆODARIA (15, the #Phæocystina#). On the other hand the following 5 orders, which are the main constituents of Radiolarian rocks, are of pre-eminent geological