GENUS SPHiEREXOCHUS. 375 



CRUSTACEA. 



SPH.^REXOCHUS ROMINGERI. 



PLATE 22, FIGS. 4-7. 



Sphcerexochus mirus,of authors; not S. mirus of Beyricii. 



" " page 30 of original paper; p. 334 of present Report. 



Sphcerexochus romingeri : Hall, Geological Report of Wisconsin, p. 434. 1862. 



A farther careful study of this species, with larger collections for com- 

 parison, has shown certain differences in tne form and proportions of the 

 head, size of the cheek, etc., warranting its separation from the European 

 species. The annulations on the axis of the pygidium are not so abrupt, nor 

 the posterior extension so great ; while the lateral lobes are more free at 

 their extremities, giving a very different aspect to this part of the fossil. 

 This fossil is pretty widely distributed, occuring at nearly all the localities 

 of the Niagara group in Wisconsin and Illinois. 



ENCRINURUS NEREUS (n.s.), 



PLATE 21 (12), FIG. 15. 



Encrinurus (sp.); P- 30 original paper; p. 334 of present report. 



Pygidium triangular; length and breadth about equal. Axis sharply 

 elevated and marked by about eighteen rings, with a farther extension 

 upon which no markings are distinguishable. The lateral lobes are 

 marked by eight or nine distinct costae, which, in the cast, are not 

 tuberculated. 

 This species differs from the one in the Clinton group of New- York, in 



the greater number of ribs on the lateral lobes of the pygidium., while 



there are fewer annulations on the middle lobe. 



Formation and locality. In limestone of the age of tlie Niagara group, 



at Racine, Wisconsin. 



DALMANIA VIGILANS. 



Reference, page 31 of original paper, page 835 of this Report. 

 PLATE 21 (12), FIGS. 16, 17 & 18. 



General form of body not determined. Cephalic shield convex, semi- 

 elliptical, the breadth about twice as great as the length (exclusive of 

 the frontal projection) ; the border is extended in front into a triangular 

 flattened process, the base of which is little less than one-half as wide as 

 the width of the anterior portion of the glabella. In older individuals 

 this projection becomes more obtuse and sometimes rounded; the lateral 

 borders are broad, flattened, separated from the cheeks by a distinct 



