Reviews — Bigsbys Thesaurus Siluricus. 23 



Echinodermata. — The earliest seas give us also, wherever they are now trace- 

 able, countless forms of this class. In the order Crinoidea, 78 genera and 315 

 species are recorded from the many regions where the Silurian rocks containing this 

 group are known; the Cystideans, 33 and 136 species ; ihn Aster idea, 14 and 90 

 species, in all 512. Deep interest must always be attached to the distribution 

 and development of this class. The Lower and Upper Silurian stages over 

 the entire world possess a rich assemblage of genera, perhaps the Niagara group of 

 America, the Wenlock Rocks of West Europe, and especially England and Wales, 

 contain the most remarkable forms of Crinoidea known. They are brought to- 

 gether and catalogued in such a manner in the Thesaurus, that we can readily 

 mentally restore the old Silurian submarine Crinoidal forests, and whatever may 

 have been the nature of the water or sediment in which they flourished, we are led to 

 examine and weigh with much interest the results embodied in Table K [Geographi- 

 cal Summary] compiled from the 1 1 pages of the Great Table. The comparatively 

 limited geographical range of some genera, and the colonisation of different areas 

 (widely separated) by the same genera, are problems of high interest to the physicist 

 and naturalist,' and the distribution of moderngenera in the Caribbean area, Australia, 

 theWest Indies, etc., may throw somelightupon these remarkable forms of ancient life. 

 America seems to have had two chief foci of concentration widely separated, one in 

 the west, over an extensive old marine area, resulting in the rocks of Illinois, Wis- 

 consin, and Tennessee ; the other to the east, in Canada West, and the Northern 

 part of the State of New York.* 17 American Silurian areas are enumerated in the 

 table, showing the wealth or poverty of each, dependent perhaps upon diligent 

 research on the one hand, or condition of sea, etc., non-favourable to life, and 

 development on the other ; such, however, is the state of our knowledge at the 

 present time as to the distribution of this order in North America. Three chief areas 

 in the Western Hemisphere abound in the CHnoidea and Cystidea, (the British 

 Islands, Russia, and Sweden), and chiefly in the limestone of the Upper Silurian 

 stages,— the Wenlock Rocks of England and Wales, and the so-called Coralline 

 Limestone of Russia yielding the richest harvest. The unequal distribution of the 

 whole class is singularly detailed in the Thesaurus, which clearly suggests the 

 want of research in given regions. Thus : 



Only one form {Edrioaster) is known in Nova Scotia. 



J, Crinoid {Mariacrinus) is known in India. 



,, Scyphocrimis ,, Sardinia. 



,, Hypanthocrintis ,, Scotland. 



,, Crotalocrinus ,, Arctic America. 



In Spain we only know of two forms, both Cystideans ; in Norway, only nine 

 Crinoids and one Cystidean ; and in the classical Silurian district, Bohemia, one 

 Crinoid or^y—AsocHnus, and 12 Cystideans ; these facts may be termed curiosities 

 of distribution, and will remain so until we know more of the areas and their faunas, 

 through future research. 



Cephalopoda. — The names, range, and distribution through the Silurian rocks of 34 

 genera, and 1419 species, of the Tetrabranchiate, — Odontophoj-a close the Thesaurus. 

 It is rendered still more valuable through the liberality of M. Barrande, who placed 

 his MS. list of this great group at the disposal of the author ; thus some 500 species 

 are here notified and stratigraphically placed in the Bohemian Rocks, prior to the 

 completion of Barrande's own work upon the Cephalopoda of the Bohemian Basin. 

 It is impossible to omit notice of these gigantic Lower Palaeozoic pelagic Ortho- 

 ceratites, whose remains swarm in both the Upper and Lower Silurian deposits of 

 every known region of the globe. 37 areas are enumerated in the Geographical 

 Summary at p. 191 in the Thesaurus, 18 in America, and 19 in the Western Hemi- 

 sphere ; two genera contain collectively 102 1 species — viz., Cyrtoceras, 317, and 

 Ortheceras, 704 ; the former distributed through 22 countries, the latter 36. As- 

 suming, which we do not doubt, the transcribed correctness and compilation of 

 the author, the summary of this group is exhaustive ; 22 pages are occupied by the 

 genera and species which are spread through every Silurian deposit known, their 

 universality in deposit and area, and widely spread distribution, demonstrates and 



^ See the works of Hall, Haydan, Meek, Billings, Schumard, Worthen, De Koninck. 

 2 21 Genera are common to the Western and Eastern hemispheres; 35 are peculiar to 

 America ; and 23 are European, 



