I 



I;KO.\TKIIM . 



ana Hl.'MNTKl s. <M,idfu-. ls:','.i (cm. 

 I'.K.IS i n - /.'<///;/ 



i i.i, K'-| 



i/ruji /un.ifii- HII.I.IM.-, ]gi3. G 



nleii.i IttH'ilu* is the the genus known in America. 



ami the only -pecie- \et de.-crided from the lower Silurian rocks of this country. 

 The character* of thf s\ '\ \>y Hillings, his originals coining 



from the Trenton lime-tune of nttawa where, as sail I l>y him. it i- not of infrequent 

 occurrence. In thr : Camel an excellent wood-cut of an entire 



individual \va.- given. 



Thr -iiecimen^ from Minnoota. while all more or less incomplete, agree 

 throughout with the <'anadian species ami we have therefore introduced Milli 



HronttH* /mi.. 



figure a- m to the student than any which might \te derived from 



the 1 1 before u>. The latter <>: a somewhat hroken individual having 



tin- part.- togi-ther fnun the Trenton lime-tone near Spring Valley, Minnesota (No. 

 U>71 of the Mii-enm collection), a -rani'lium from the tiah-na limestone at Wykoti 

 (Mr. I'lrich's collection), and a line external impres-ion of a pygidium from the same 

 locality (Ir. KohhinV collection). 



Throughout the specie- of - then- is a certain homogeneity in -tructure 



which rend. ..-neric group more comp;i. -harply delimited than i> n-ual 



among the trilol>it-. Hut few sugge>tion- ..f ;t divi.-iou of the genus havi- been 



made and only one of the propo-ed suliordinate generic term- has met with even a 



; al acceptance. Thi- i- 7V, //>. one of COP; .-, dt-igm-d to include 



;es with marginal spines on the pygidium. and which ha.- demo: 'itle 



to recognition, -ince the group ha- proven to possess a .|iiite definite .-tratigraphical 

 value as a structural variation prevailing in Hercynian faunas. 



In II. litnntii* the \arion- [lart.s were not irr, .opment of any 



unusual character-. The - >OS8688 a -h> <in the pygidium. which -hou- 



