CONTRIBUTIONS TO PALAEONTOLOGY. 1G3 



Pygidiubi siibqiiadrilateral, with strong but slender diverging 

 spines from the posterior angles. The axis and lateral lobes, 

 without tlie expanded border, are semicircular ; the axis some- 

 what abruptly elevated, with five annulations : lateral lobes 

 \vith five segments, including the anterior one. The border ex- 

 tends from the extremity of the anterior segment in a direction 

 nearly vertical, or slightly expanding downwards : the poste- 

 rior edge of the border extends below the termination of the 

 axis about one-fourth the entire length of the pygidium. 



The measurements of three individuals give following dimensions : 



I. II. III. 



Length of glabella in front of occipital ring .. .23 in. .46 in. .63 in. 



Width of glabella at base 20 .47 .60 



Width of glabella at apex 13 .28 .37 



Length of frontal limb 09 .15 .18 



Entire length of head 37 .71 .94 



The proportions continue very nearly in all the parts except the frontal limb, which, 

 in the larger one, has but twice tlie length of tlie smaller one. while the other parts 

 are about three times as great. Since we find similar fragments of thoracic segments, 

 and portions of the pygidia associated in tlie same specimens with the glabella, I can 

 have no doubt of their identity with C. iowensis. 



The illustrations en Plate viii, f. 10-12, are from Trempaleau, and are 

 of the largest individuals found there. Subsequently Dr. Shumard has sent 

 to me specimens of the glabella and fixed cheeks of several individuals from 

 Black river, which are much larger. These are illustrated on Plate vii, 

 f. 30. 



^ At the mouth of Hoot river this species occurs of much larger dimensions 

 than the specimens of Trempaleau, and considerably larger than those from 

 the Black -river locality. The Root - river beds are apparently somewhat 

 higher in the series than thosf". of Trempaleau or Mountain inland ; but 

 beyond this and one other species, I have not identified fossils from that 

 locality. 



The G. ioivensU is a well-marked and very characteristic species of the 

 lower fossiliferous beds of the Potsdam sandstone. 



Dr. SilUMARD remarks that " this species may be readily distinguished 

 from the CrepicephaJiis [ConocephalUes] loisconseihsis, Owen, to which it is 

 somewhat nearly allied, by its wider and more conical glabella, and much 

 narrower front margin." 



This fossil occurs with ConocephalUes minor, Lingula, Obolella? 

 and TiiECA, at Trempaleau ; and in a similar association, near the mouth 

 of Black river in Wisconsin. The larger specimens, from Root river, are 

 associated with fragments of Trilobites, among which no other fossils have 

 been observed. 



