150 Jlic JJ/e-Historij of Sjn'rffcr JievU. 



this eoiiiiection, Hall's remai'k in Urst clause of p. 23T, 4th 

 ToL, Pal. ISJ^. Y.) from our Sjjirifer Icevis through S. fimbriatus, 

 and others, to the Silnrian S. crispns, and recognise the same 

 grades and variations in the forms appearing on the other side 

 of the Atlantic, Tip to the Carboniferous forms. 



What does this series of observations suggest ? 



Whatever theoretical description we may give to sjjecies, here 

 are. in the lirst place, an abundance of individual organisms 

 whose remains are fonnd in the Upper Silnrian rocks of Europe, 

 Great Bi-itain and America, jjresenting a few clearly-marked 

 distinctive characters, variously developed in the individual 

 forms, bnt so grading in the several varieties as to cause careful 

 naturalists to associate them as varieties of a single species. 

 There are well-marked tyi)ical characters distinguishing all the 

 individuals from other forms of the same genus, together with 

 great variability of the characters themselves. In the upper 

 part of the Upper Silurian we tind the same typical characters, 

 with a greater permanence of one or other of the variations; but 

 still, in the variations occurring later in the Corniferous and 

 Hamilton, we have the main type represented with some variations 

 strongly marked and seemiiig to be fixed, but still recognised as 

 varieties simply. 



In the Portage, we see under peculiar conditions a solitary 

 race of the type with greatly e.xnggerated size, — a luxuriant form 

 but still presenting the typical characters of the second varie- 

 tal type. 



In the Carboniferous we meet with several well-marked va- 

 rieties, but no feature which did not appear in the early form 

 except large size, which is evidently a mark of good nourishment 

 and other good conditions of growth. This latter seems to be a 

 character of most of the Carboniferous forms of Brachiopods 

 which have lived on from earlier times. There may be unknown 

 characters to distinguish these forms, but of the characters that 

 are preserved we have evidence that in the eai'liest form, the 

 type, S. crispus, His. of the ^Niagara, etc. (with its varieties), 

 are found all those which afterward appeared in the later repre- 

 sentatives. 



These characters appeared in combination in a single group 



