TKII.OI.II i V":; 



-pi-cimen- t In- -ami- fart hold>; tin- largest , all' I indeed t he only well deli ned -periim-n 



"f /. 'iiat I have -een lias a length of IMI nun. Tin- smaller >| miens of the 



-ame type, so far as their preservation permit- the determination, possess cheek 

 -pines. 



'-.-Itoteltu intJ-imu* L-x-k.-. Hiifl-mi Itiv.-r (jnniji. Granger. 



It would appear that among the specimens from the Hudson River group of 

 Ohio. Indiana ami Illinois, this is not always the case, as Locke's immense original 

 ami its specific name itself indicate.* Here, locally, the occurrence of large fragments 



iiiniferou- heads is not altogether infrequent, perhaps even predominant with 

 reference to the aspinous heads; but whether the rule or the exception in that 

 locality, it need not modify the purport of our argument. 



The morphological significance of the cheek spines in the trilobites has not 

 been demonstrated, nor have they invited especial attention. Undoubtedly their 

 significance varies in different groups. In this group with the evidence now at 

 haii'I. we iiii-1 a suggestion of their meaning. To present these points with the 

 greater lucidity a few general remarks will be appropriate, bearing upon the 

 developmental characters of the species under consideration, and upon the phylogeny 

 of the asaphs. 



In fxotrlus imuriniHs. a<lvaiieing growth is accompanied by gradual obscuration 

 of all lobation. In the average adult of the New York Trenton, as describe.! above, 

 thi- obsolescence of surface division is well advanced, but in immature individuals 

 the degree of lobatioi, ally of the parts of the pygidinm. vi/.: the dctinition 



of the axis, its annulations and the ribs of the pleura-), is proportioned inver-i- 

 the size of the animal. Voun^ entire individuals l.'i mm. in length, and many young 

 pygidia belonging to animals not much larger have the segmentation so clearly 

 developed that both ribs and annulations may be di-tinc,tly counted, the normal 

 convexity of the shield being, meanwhile, undisturbed. Sharp lobatiun of the test 



It mlKlit I tlilnk.be t f:. Miln Stare not "drawn In " from KMMn 



att then. Without Impucnlnx t 

 oriclnal. If cirrvctlj raprevraMd. < 



