484 PAL,E0NT0L0GICAL REPORT OF GEOLOGICAL SURVEY. 



External markings. The body is adorned by a most beautiful net- 

 work of raised triangular figures ; the points of the principal triangu- 

 lar figures rise from, and terminate at, the centre of the first interradi- 

 al pieces ; a subordinate set of figures terminate at the centre of all 

 the pieces below the arms. In some specimens the lines are continu- 

 ous, in others, interrupted. The summit pieces are sometimes adorn- 

 ed by a single prominent granule ; in other specimens, many of the 

 pieces are ornamented by a number of granules, arranged in lines across 

 some of the pieces in nearly parallel rows, or in a circular band around 

 a more prominent central one. 



Geological position and locality. Found in great numbers in the 

 limestone immediately over the hydraulic cement beds, Jefferson coun- 

 ty, Kentucky, on Beargrass creek; same beds on Rock Island, Falls 

 of the Ohio river, and Silver creek, Clarke county, Indiana. 



In the neighborhood of Louisville, resting on the hydraulic cement 

 bed, and below the black slate of the Denovian period, occurs a thin 

 bed of limestone, its base resting on the cement stone bed ; in this is to 

 be found a partial bed of conglomerate, of ferruginous gravel ; a similar 

 bed of conglomerate exists below the cement bed. The cement bed at 

 Beargrass creek is from four to six inches thick. Northwsetwaardly, 

 three and a half miles, at the foot of the Falls, on the Indiana side of 

 the river, this stone is eighteen feet thick ; from the bed, at the foot of the 

 Falls, large quantities of hydraulic cement is manufactured, of superior 

 quality. Resting on the cement bed, as before stated, is a bed of lime- 

 stone from four to eight feet thick ; the inferior two feet abounds in 

 crinoidce, in fact, the bed is literally made up of the remains of these 

 animals. Then succeeds, about two feet abounding in fossil corals, 

 amongst which are a few entrochites ; these are again succeeded by 

 Crenoidea, Brachiopoda, and Trilolites. Upon the whole rests a bed 

 of black slate, variously estimated from one hundred to one hundred 

 and forty feet thick. 



A few individuals of our genus, and probably of the same species, 

 occur at the base of the hydraulic beds ; these are seldom well pre- 

 served ; should these prove to be our species, the vertical range of the 

 species will be about twenty-five feet ; should they prove to be differ- 

 ent, the range will be only about two and a half or three feet. 



