140 SIXTEENTH REPOKT ON THE CABINET OF NAT. HISTOET. 



The lower surface of the pjgidium is more strongly marked thao 

 any other part. 



This speeies occurs rn tne Liglier beds of the formation ^ and usually 

 within fifty to one hundred feet below the Lower Magnesian limestone. We 

 also find a similar or identical species in the Magnesian limestone. 



In its extremes of size, this species has a wide range. The smallest head 

 which I have observed has a length of one-fourth of an inch, including 

 the frontal limb ; while the largest one has a length of more than two and 

 and a half inches^ with a width between the extremities of the posterior 

 limbs of the fixed cheeks of more than four inches. A pjgidium associated 

 with the latter has a length of two and a quarter inches, with a width of 

 more than three and a half inches. A fragment of a thoracic segment mea- 

 sures, from the centre of the axis to the extremity, more than two and a 

 half inches^ ; which would give the width of the body five inches. A pygi- 

 dium found in a loose mass of Lower Magnesian limestone near Madison^ 

 Wisconsin, by Mr.5- p^^ft^u, measures nearly two inches and three- 



t^bi fourths in length, and four inches and three-quarters in width, 



PLATE IX. 



Fig. 5. A large head from Mazomania : the frontal limb is given in form and pro- 

 portions- from another specimen^ in which it is preserved entire. 



Eis. 6. A pygidium from Lagrange isountain. 



Fia. 7. The pygidium of a large individual from the Magne&ian limestone . This one 

 presents some slight differences in the form and proportions of the axis, 

 when compared with fig. 4 of Plate xi. 



Fia. 8. A part of the thoracic segment from the Lagrange mountain locality. 



Figs. 9 & 10. Hypostomse found in the same locality, and referred to this species. 



PLATE XI. 



Fig. 1. A hypostoma associated with the specimens of fig. 5 of Plate ix aiwi fig.4.of 

 Plate xi, and clearly belonging to this trilobite. 



Fig. 3. A cheek from Lagrange mountain. Similar cheeks occur with the preceding 

 specimens, and some of them are much larger than this one; measuring 

 two inches in width in the widest part, and an inch and a half in the nar- 

 rower portion, or double the width of the one figured. 



Fig. 4. A pygidium from Mazomania*. 



The hypostoma, Plate xi, f. 1, is doubtless of this species j having been 

 found associated with fragments of several large individuals at Mazomania, 

 where I have not seen any other large trilobite. 



The specimens figs. 9 & 10 of Plate ix are from Lagrange mountain : 

 they present some differences, and both differ somewhat from the larger one. 

 All are imperfect ; the specimen figure 9 being more nearly entire than the 

 others. They belong either to the D. minnesotensis proper, or to the form 

 given in fig. 11, Plate ix ; since no other species, except the D. pepinensis, 

 and the extremely rare form fig. 12, Plate ix, are found at that locality ; 

 and the hypostoma of D. pepinensis is given in fig. 4, Plate ix. 



* This specimen is associated in the same beds with fig. 5, Plate ix ; baring been obtained 

 from the locality at a subsequent period. 



