480 HISTORICAL GEOLOGY. 



S-sided forms among them, and the thickness indicated, make a relation to the Medusse 

 doubtful. Nathorst states, however, that he has experimented with some species of Me- 

 dusae and obtained similar impressions. Moreover, some modern Medusaj have occasion- 

 ally varieties with five divisions. 



A general review of the fossils of the Lower, Middle, and Upper Cambrian will be 

 found in Walcott's papers : Bulletins U. 8. Geol. Survey, Nos. 10, 30, and 81, and I'enth 

 Ann. Bep. U. 8. Geol. Survey ; and details here are therefore unnecessary. 



See, also, papers by Billings, Palceozoic Fossils, Canada Survey ; J. W. Salter, Q. J. 

 G. Sac, XV., 551, 1859; James Hall, Sixteenth Ann. Report, N. Y. State Cabinet, pp. 

 119-184, 1863; G. F. Matthew, Boyal Soc. Canada Proc. and Trans., vols, i.-v., vii.-ix. ; 

 C. F. Hartt, in Dawson's Acadian Geology ; S. W. Ford, Am. Jour. Sc, 3d series, vols. 2, 

 3, 5, 11, 13, 15, 19, 21, 22 ; Rominger, Phil. Acad. Sc. Proc. 1887, p. 12 ; Whiteaves, Am. 

 Jour. Sc, 3d series, xvi., 224 ; Whitfield, Geol. Survey Wis., iv., and Am. Mus. Nat. Hist. 

 Bull., i., p. 139 ; Shaler and Foerste, Bull. Mus. Comp. Zool. Camh., xvi., 115, 1888 ; also 

 Walcott, Am. Jour. Sc, xxxiv., xxxvi., and U. 8. Nat. Mus. Proc, vols, xi.-xiii. Besides 

 the above, there are recent studies of the Genera of Cambrian Brachiopods by Hall and 

 Clarke {Pal. N.Y., vol. viii., 1892); a paper on the Classification of the Brachiopods by 

 C. Schuchert {Am. Geologist, March, 1893) ; and a paper on the Development of Brachio- 

 pods by C. E. Beecher {Am. Jour. 8c, xli., 1891). Beecher separates from the genus 

 Kutorgina of Billings (the type of which is K. cingulata, an articulate Brachiopod) the 

 species Kutorgina (Oholus) Lahradorica of Billings, var. Swantonensis of Walcott (which 

 is inarticulate and undergoes no modification of form during growth), and makes it the 

 type of the new genus Paterina. 



The investigation of the Cambrian rocks, in late years, has greatly increased the 

 number of known species. An extended description of the Lower Cambrian fauna is 

 published in the Tenth Ann. Beport of the U. S. Geol. Survey, 1890, by Walcott. Mat- 

 thew has described many species of the Middle Cambrian, and the Upper Cambrian faunas 

 are being studied by Walcott. Over 100 genera and 400 species are already described 

 from the Cambrian of North America. Walcott gives the following table of the number 

 of genera and species of fossils in the Lower Cambrian alone of North America (1890): — 



Gen. Sp. Gen. Sp. 



Spongiozoans 4 4 Brachiopods 10 20 



Hydrozoans 2 2 Gastropods 6 15 



Actinozoans 5 9 Pteropods 4 15 



Echinoderms 1 1 Trilobites 15 51 



Tracks, trails, burrows . . 4 6 Other Crustaceans ... 5 8 



Total . . 56 131 



Adding species not included above, mostly described by G. F. Matthew, of New 

 Brunswick, the total number of American genera is nearly 70, and of species 170. 



FOREIGN. 



The Cambrian rocks of Great Britain outcrop in North and South Wales, 

 and in Shropshire, just east of Wales. The principal regions identified by 

 fossils are the Longmynd, of slate and grits, in Shropshire ; the Harlech, 

 and the Bangor and Llanberis toward the Menai Straits, of sandstones, flags, 

 and slates, in North Wales ; the St. Davids (ancient Menevia), of sand- 

 stones, slates, grits, and conglomerate, in South Wales ; and that of the 

 Malvern Hills. In Ireland, Cambrian rocks occur at Bray head and in Wex- 



