FACTS AND OBSERVATIONS. xix 



with its nine species. It is confined to Decatur County, Tennessee *. On the other hand, although 

 the species of a genus may be few, they may, contrary to rule, be widely scattered. In this way 

 the three species of Scyphocrinus are found in New York, Sardinia, and Sweden. 



Crinoidal species are very local, with a few exceptions. Thus the single species Marsupio- 

 crinus ccelatus lived in the Silurian seas of England, New York, and Tennessee. Calliocrinus, 

 Crotalocrinus, &c. present similar facts. 



In this order zoological connexion between areas is chiefly maintained by genera. Twenty-one 

 genera are common to the western and eastern hemispheres a fact of weight; thirty-five are 

 exclusively American ; and twenty-three are European. 



Two hundred and forty-five species are North- American, and one hundred and fifty-eight are 

 European, which reverses the usual proportion of fossil life in these two great divisions of the earth. 



Recurrence is rare among Crinoidea. I only know of twelve instances, six of which are given 

 in the footnote f- Many of them are in coterminous beds. 



Cystidea. The Tables K and L, just referred to, contain much information respecting this 

 beautiful and curious order. It consists of 32 genera and 136 species. Until within the last thirty 

 years little was known about it. Since then this order has been illustrated in an admirable manner 

 by Von Buch, Forbes, and Billings. 



Its genera Palaocystites, Protocystites, Trochocystites are found in Primordial strata at 

 Phillipsburg (Canada East), at the head of Lake Champlain, at Montreal?, in the Mingan Isles 

 (Gulf of St. Lawrence), in South Wales, in Spain, and Bohemia. It abounds in the Trenton 

 Limestone of America, in the Caradoc beds of Britain generically and specifically, passes freely into 

 Upper Silurian, and then into a Devonian Limestone. 



In both hemispheres the Cystidea have the same two headquarters as the Crinoidea; but 

 America exhibits fewer species than Europe. Edward Forbes, by way of directing particular atten- 

 tion to these gatherings, calls them polarizations. 



The Cystidean genera are rather more prolific than the Crinoidea ; but eight have each only one 

 species, even after a close inquiry for them. The geographic range of species is less also. Out of 

 thirty-three countries inhabited by Crinoids, in only twenty have Cystidea been observed. 



The proportion of appearances in different lands to species is as six to five. 



Here again, the genus Holocystites, with its seven species, never leaves Wisconsin, with the 

 exception of H. sphcericus, which we have at Chicago (Illinois), a bordering state. 



Nine genera are common to Europe and America, ten being exclusively American, and eleven 

 exclusively European. At present Cystidea have not been brought from India or Australia. 



Apiocystites Huronensis affords the only known instance of vertical range in this order ; and it 

 is short and doubtful. 



Asteridea. This order contains fourteen genera and sixty-one species, or four to a genus; 

 while in Brachiopoda it is thirty species to a genus, in Cephalopoda thirty-three. Palaaster 

 contains fourteen species as the richest genus, Edrioaster and Palcechinus having each one only. 

 This order is only seen in nineteen Silurian areas. 



Europe and North America have five genera in common ; five others are the sole property of 

 America, and four of Europe. 



In America we find, again, the chief abode of the Asteridea to be around the City of Ottawa 

 (Canada West) and in North-west New York State (twenty-one out of thirty-three species) . Else- 

 where the species are scattered singly or in pairs, in Indiana, Ohio, Illinois, Canada, Newfoundland. 



* Genera and species may seem far apart geographically, when in reality they are close together, as on the oppo- 

 site sides of a boundary river, the St. Lawrence or the Mississippi. Thus two species of Stephanocrinus are on the 

 same sheet of rock, but are catalogued as in two separate countries. 



t Ctenocrinm typus, Cyathocrinus exilis, Melocrinites Icevis, Pleta, Corall. Lst. ; Dictyocrinus squamifer, H. R. G., 

 L. H. G. ; Glyptocrimis decadactylus, Primordial (Geinitz), H. R. G., CL. ; Periechomnus moniliformis, Llandov., W.L. 



