146 Cincinnati Society of Natural History 



3 — The development of the marginal rim of the cephalon is 

 less pronounced, the intramarginal groove being of less depth and 

 width. 



4 — The intramarginal groove of 'the pygidium is so much bet- 

 ter developed that /. covingtonensis may be distinguished by this 

 moderately developed border, while the intramargmal groove of 

 /. benjamini is relatively obscure or practically absent. 



Isotelus benjamini was identified by Ulrich among specimens 

 collected at localities between Sadieville and Rogers Gap, Ken- 

 tucky. The specimen represented by Fig. 13 on Plate I came 

 from locality 54.5 miles from Ludlow. The facial margin an- 

 terior to the palpebral lobes is not indicated in this figure. It 

 curves regularly forward to within a short distance of the margin 

 of the cephalon and then takes a course parallel to the latter. 

 Fig. 5, on page 145, indicates the curvature of the dorsal side of 

 this free cheek, seen along a transverse section from a point an- 

 terior to the palpebral lobe. The same species occurs also at 59.1, 

 59.5, and 59.7, and was identified by Ulrich with less certainty 

 from the locality one mile north of the railroad station at 

 Cynthiana. 



Isotelus covingtonensis was identified by Ulrich from the lo- 

 calities 59.7 and 59.1 miles from Ludlow, near Rogers Gap, and 

 also from the locality one mile north of Cynthiana station. 



44 — Trinucleiis concentriciis, Eaton — This species occurs at 

 localities 60.3, 59.1, 58.3, 57.8, 57.4, 56.8, 56.4, 55.3, 54.8, and 54.2 

 miles from Ludlow. At Cincinnati it occurs not only in the lower 

 half of the Eden, but also in the 20 feet of strata immediately 

 underlying the Fulton layer. The layers containing Eridorthis, at 

 Brent, belong distinctly below this Trinncleus horizon. 



45 — Proetus sp. — The middle part of a cephalon, 6 mm. long, 

 and lacking the free cheeks, was found at the railroad cut north 

 of Cynthiana. It closely resembles Proetus undid ostriatus, Hall, 

 as figured by Dr. Ruedemann, possessing also the microscopic 

 transverse lines, whatever these may indicate. However, the oc- 



42 



