292 PROCEEDINGS OF THE ACADEMY OF [1889. 



Straparollus ; but these require no consideration in the present 

 connection. 



In the majority of cases the carina? or angular prominences on the 

 whorls of the Burlington Straparolli appear to be simply thickenings 

 of the shell at those points. The internal transverse section is 

 circular, as shown when the shell is removed from the matrix form- 

 ing the cast of the inside. Some species have a thickened shell, 

 with the whorls barely in contact, or even separated toward the 

 aperture. In instances of this kind the internal casts have much the 

 appearance of some of the forms for which Sowerby established the 

 genus Phanerotinux. But with the latter have evidently been included 

 a number of evolute Straparolli. 



Straparollus latus (Hall). 



Euomphalus latus Hall, 1858. Geol. Iowa, vol. I, p. 605. 



Shell rather large, discoid, composed of four to five rather rapidly 

 enlarging volutions, plane above ; spire nearly on a level with 

 the upper surface of the outer whorl ; suture impressed ; deeply and 

 broadly umbilicate ; aperture nearly circular, flattened above. The 

 broad flattened area occupying the upper surface of the volutions is 

 bordered on each side by a distinct carina, the inner being near the 

 sutural line. Below the outer ridge are sometimes two scarcely 

 perceptible angularities — one around the periphery and the other 

 along the middle of the whorls below. The latter, as shown in 

 young specimens, is often well defined, but after the shell has become 

 half-grown the obtuse prominence becomes obscured. In some 

 specimens the ridge above the periphery is so pronounced as to leave 

 a narrow concave area immediately beneath. Straparollus latus is 

 the most characteristic form of the genus occurring in the Burling- 

 ton, but it is not very common. It attains a maximum diameter of 

 eight centimeters. 



Metoptoma t umbella Meek and Worthen. 



Metoptoma (Platyceras f) umbella Meek and Worthen, 1866. Proc. 

 Acad. Nat. Sci. Ph'ila., p. 267. 



Metoptoma? umbella Meek and Worthen, 1868. Geol. Sur. 

 Illinois, vol. Ill, p. 506. 



The generic relations of this and several similar forms from the 

 Lower Carbonic .rocks of the Mississippi basin are not clearly 

 understood. The species in question do not appear to properly be- 

 long to Metoptoma, as originally characterized by Phillips, in the 

 Geology of Yorkshire, and as typified by his M. pileus and M. 



