NIAGARA LIMESTONE OF CHICAGO, ILLINOIS. 103 



rounded angle of about 100°. The distance from the summit of one ridge to that of the 

 next, measured on the dorsum, varies from one third the transverse diameter of the whorl, 

 to considerably less. The space between the ridges is nearly flat, and in the cast — but 

 not on the shell — discloses indications of two low, barely perceptible ridges. The last 

 chamber seems to be entirely destitute of surface ornaments, except incremental lines, 

 which are sinuate dorsally, to correspond with the ridges. There are indications that the 

 aperture was correspondingly sinuate. The position of the siphon has not been observed, 

 but a feeble depressed line or shallow furrow runs along the back of the cast, visible be- 

 tween the ridges, and creating a suspicion that the siphon is in close proximity. 



Dorso-ventral diameter, .78 inch at a place where the transverse diameter is .73 inch ; 

 distance between the ridges on the dorsum, at the same place, .25 inch. In other specimens 

 the ridges are more approximated. 



This species differs from Gyroceras (Lituites) americanum Billings, in not being flattened 

 on the back, and in the course of the annulations. It differs from Lituites giganteus Sower- 

 by, in having the annulations extend quite across the back without any diminution in size. 



Named in recognition of aid received from Henry Bannister, a zealous and promising 

 young geologist of Evanston, Illinois. 



Lichas Dalman. 



Lichas pugnax W. and M. 



Plate III. figure 10. 



Body large, outlines unknown. Glabella somewhat parabolic in contour, prominent, with 

 a middle lobe and two lateral ones on each side. Middle lobe consisting of two regions, 

 the anterior of which has a triangularly rounded base, and in the centre is extremely prom- 

 inent, the front margin descending precipitously to the border ; the posterior region is de- 

 pressed and cuneately produced backward between the lateral lobes, diminishing in the nar- 

 rowest part to one fifth the greatest transverse diameter of the anterior region, and then 

 widening behind the approximated ends of the lateral lobes. The lateral lobes are oblong- 

 elliptic, slightly flattened on the outer side by the eyes, less prominent than the middle lobe 

 and separated from it by deep valleys ; these lobes are twice as long as broad, and their lon- 

 gitudinal axes lie at an angle of 36° with the axis of the middle lobe. The ocular lobes 

 are smaller and more depressed than the last, and lie against their outer sides a little pos- 

 terior to their middle, being deeply separated from them. The border is thick and narrow, 

 regularly curving around the middle lobe of the glabella, and is not produced in front into 

 a proboscis. Occipital ring very prominent and broad; furrow deep. All parts of the 

 glabella are covered by a granular crust. 



The thorax is imperfectly known. It appears from some specimens that the axis is prom- 

 inent, and from numerous others that the lateral lobes are broadly expanded and im- 

 perfectly articulated, though the crust covering the pleune is deeply furrowed between the 

 joints as well as along the middle of each pleura. Some of the articulations, undoubt- 

 edly posterior ones, become very broad and flat. Every portion of the thorax seems to 

 have been covered with a separable, coarsely and unequally granulated crust, the granules 

 or eminences of which are directed backwards, as in other species of the genus. The basis 

 of the crust is marked by irregularly wavy, somewhat continuous, imbricated furrows, 

 which seem to run nearly parallel with the general outline of the body. 



