120 



Contributions to Palceontology. 



than four inches. A pygidium 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 measures, 

 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 pygidium found in a loose mass of Lower Magnesian limestone 

 near Madison, Wisconsin, by Mr. S. V. Shipman, measures nearly 

 two inches and three-fourths in length, and four inches and three- 

 quarters in width. 



PLATE IV. 



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

 and proportions from another specimen, in which it is preserved 

 entire. 



Fig. 6. A pygidium from Lagrange mountain. 



Fig. 7. The pygidium of a large individual from the Magnesian limestone. 



This one presents some slight differences in the form and pro- 

 portions of the axis, when compared with fig. 4 of Plate vi. 



Fig. 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 VI. 



Fig. 1. A hypostoma associated with the specimens of fig. 5 of Plate iv 

 and fig. 4 of Plate vi, 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 narrower portion, or double the width 

 of the one figured. 



Fig. 4. A pygidium from Mazomania. 1 



The hypostoma, Plate vi, f. 1, is doubtless of this species; 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 iv are from Lagrange moun- 

 tain : 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.rninneso- 

 tensis proper, or to the form given in fig. 11, Plate iv; since no 

 other species, except the D. pepinensis, and the extremely rare form 

 fig. 12, Plate iv, are found at that locality ; and the hypostoma of 

 D. pepinensis is given in fig. 4, Plate iv. 



^his specimen is associated in the same beds with fig. 5, Plate iv ; hav- 

 ing been obtained from the locality at a subsequent period. 



