-hales .1 rithony Park ami from .Minneapolis have nine, ami a single coiled 



example from tin- (Jalena sh.i fan, 'ioodhno. county. Minnesota, haw Imt 



ei^ht. The<e ii 86 in degree of segmentation, DBMOOmpanittd by any palpable 



di-tinction in other resperts do not, aflord a l-a-i- of -pecific reparation. They are 

 apparently only developmental condition-, not of the. individual so much as of tin- 

 -perilic tV] 



Ainont: all the western specimens examined there is no great difference in size. 



None are larger than the specimens from Trenton Kail.- 1 tea ring ten segments, and 



B from the lilack Kiver limestone with nine. The habit of the western specimens 



mewhat -mailer, though separated heads from Dixon, Illinois, attain the usual 



"f the New York . \an N T one of the specimens from Minnesota appear to 



possessed ten segment-, and tin- local variation i- -imilar to that occurring 



aiming the Canadian examples. 



Such variation- in the degree of segmentation are not, indeed, usual in the 

 mature conditions of a ipedes; they are, however, altogether in harmony with the 

 law - of morpho^eny. and deviation- from the normal Trenton type with ten segments 

 are to be interpreted a- phylogeneticallj immature or senile phases of the specific 

 I nder the description of Illtrnus milleri the detailed structure of this species 

 has been clearly given by Rillings, 



an enm'.led individual Fitf. 35. Profile of the same specimen. 



Of BumttJttu* trtntonen* <\* (sp.). x2. 



A peculiar feature which /'. fnmlMMItMf pOOMMB in common with Ii. 



is a pair of lunate depressions on a transverse line between the eyes. These are 



longitudinally elongate, each about half way l>etween the eye and the axial line, and 



much more clearly apparent on the cast than on the outer surface. It seems 



aide that -uch cepha * were areas of insertion of muscular bands 



bed to -imilar -cars on the inner surface of the hypostoma. 



mally there is no trace of longitudinal lobation on the cephalon or pygidiura, 

 and the axial furrows of the thora <'ry obs< ~ light vertical compression, 



howevt" .mally to ernp! hese features in the head and thorax, 



and -en- th- \ityoftheformer. 



Formation uml Icnilil;, n linxtit' 



. \\ -hales: Pleasai . DUD Fall* 



