TKII.'|:ITES. 



i. 



specimen from the Trenton hori/.on of New York of about the sa ..... *i/o as the 



_-oin^r then' i* no (pine, but at the angle of the eheek then tm<-t 



Kitf. 6. Genal .-\!r. initv '. 1 i.itrlu* gigai muximiM, with iumut<- spiiiuli-, . 3. 



of the te-t. making a >mall, ;wuU? tubercle. Tins evidence goes to indicate that the 

 cheek -pine in these a-apliid> is a character of immaturity, diminishing in size as 

 the U'luH romlitinii i a|i|iroaclu>'l. 



7. Onl extremltjr of Itotrltu gigatmaximtu, with pi. ut asjilnous ap-x. Trentoo 



X V 



In the earlier representatives of this generic type where segmentation of the 



pygiiiium is retaiuo-l at maturity i I'ti/rhopyge), the long cheek spines are also retained, 



i>hn< mmiiKjfri Walcott, of the Hlack River limestone; and, as observed above, 



tlir adult fon-lition of sm-h -pi-rif- i< to be regarded as. phylogenetically immature. 



-pora'iic or restricted local appearance of genal spines in large individuals, an 

 occurrence of rarity, is a natural exception to normal processes, the retention of 

 infantile characters at maturit i n>-umption in the senile condition, occurring 



alike in individuals, species and races. The / -mnfis \Vliitfield, gp., is an early 



Trenton (Hirdseye) or Calcifi-roiH form, very closely similar in all >pecific values to 

 /. .V Mining, however, at maturity cheek spines, without the segment- 



ation of fh> ivphaloti an-i jiy^idium. < >ur acqiiaintance with this form is essentially 

 restri- t.'.l to the single large, enrolled, distorted and otherwise imperf" men 



described Ky Mr. K. 1'. Wliit lieM. Toward tln> close of tlie Trenton epoch and during 

 the predominance of thenorrna! type and with t ho st-nilo decline of the race, the 



highly segmented and spiniferous type roapp.-ar- in the .1 /M./(//-;I>/> < 'liaprnan 



and the ' /irx ulrichami gen. et. sp. nov., lioth from the hori/on of the Utica slate, 



lth recurrent /Vy.7/ ( (yiy7^(ir a senile reappearance of the immature individual type.* 



id tto opportunity f ulopiol nf Iti iji In 



'irofif rama (Journal " r.i ; .i. -.1 i-. ,i .1 .1 ...... ' 



trmt In Ihc number of IrnMs fn.m li 



pulled bj ft rrwirplton (r otorurmlkMI of tlio Itnaf*. And la ooaqiM90*. by A ratom .nllto 



rotidlll.*. TbFcoarliulim*rdrlrMl frum II. . -n ..f T.I numlwr 



45 



