PALEONTOLOGY. 265 



smaller forms with eyes ; fourth, the Paradoxides. This table is found 

 also in the Royal Society paper (107). 



In the paper (109) in the Canadian Kecord of Science the author dis- 

 cusses the cliaracters of Ptychoparidw and Ellipsocejyhalida', which are 

 dwelt upon more at length in the paper, above referred to, in the Trans- 

 actions of the Royal Society. From the study of the head-shield of the 

 young of several genera, the author concludes that tliey have the fol- 

 lowing relative rank to each other, those whicii show the more primi- 

 tive features coming first, viz: (1) Ellipsocephalia, (2) Agranlos, (3) 

 Liostracus, (4) Ptychoparia, (5) Solenoplenra. 



In the fuller jjaper in the Transactions of the Royal Society (167) the 

 author describes the following species : 



Paradoxides regina, p. 119, pi. iii (nat. size). 

 EUijysocepliahts, sp. ? p. 129, pi. ii, f. 8 a-c. 

 Agraulos (f ) Whitjieldianus, p. 130, pi. ii, f. 1 a-f. 



var. compresfia, p. KU, pi. i, f. 1 g-i. 

 Strenuella (f) HaJliana, p. 132, pi. i, f. 2 a-m. 

 Solenopleura Acadica, var.elongaia, p. 1.59, pi. ii, f. 0. 



Plates i and ii illustrate series of young forms of the following gen- 

 era : Agraulos, Liostracus, Ptychoparia, Solenopleura, and ElUpsoccplia- 

 lus. 



The tabulation of the trilobites of the acadian is given as in the 

 paper (173) above referred to, and the autiior separates Microdiscns from 

 Agnostus, considering the former to be in advance, in degree of develop- 

 ment, of Agnostm, to present more variations of form, and to possess 

 a greater range of variability iy the number of rings in the axis of the 

 pygidium. Tl)e third and fourth groups show a change in the eye lobe; 

 the fourth group completes this change earlier in its development than 

 does the other. The granulated test is regarded as indicative of the 

 earlier species of Paradoxides. The author remarks upon t he very great 

 importantanceof the early stages of Agraulos, TAostracns, and Soleno- 

 pleura, "as showing the plastic condition of the organism in tlie initial 

 metamori)hoses. One has oidy to note in the series of embryonic and 

 larval forms how difi'erent the embryos are from the adult; and yet to 

 observe also how soon the generic and even the specific types become 

 visible in the larval head sliield, to be satisfied that tlie main potentiality 

 of development is in the embryo and the embryonic stages of the 

 organism." 



The period 18<S7 and 1888 is notable for the accumulation and clear 

 presentation of facts to sliow the impropriety of tlie retention in our 

 geological nomenclature of the name "Taconic system" of Emmons. 



The discusion of the subject has been continued for half a century, 

 and many of the ablest geologists of the country have been engaged in 

 it, starting with Messrs. Dewey, Eaton, and Emmons. It was origi- 

 nally proposed by Emmons as a subdivision including the rocks lying 

 below the " Champlain Division " of the "New York system" and above 

 the Primordial rocks. Messrs. II. D. Rogers, E. Hitchcock, Mather, 



