No. 189.] 55 



PLATYCRINUS GRAPHICUS (n.s.). 



Body subhemispherical, rounded below, the basal plates making 

 less than one-third the height of the calyx. First radial plates 

 wider than high : second radials broad and short, subpentago- 

 nal. Anns comparatively long and slender, composing a double 

 series of plates rising from the second radial in two pairs; 

 giving, as far as can be determined, four arms from each ray. 



Surface of plates obscurely marked by radiating lines of nodes. 

 Column composed of alternating thicker and thinner joints. 



This species differs from the P. contritus in having longer and more slender arms, 

 and but four from each ray. The calyx also differs from that one in being nodose, 

 at least on the radial plates; and the basal plates are smaller, and destitute of the 

 projecting rim at their lower margins. 



In the separated basal portions, and in the first radial plates, this species bears 

 some resemblance to P. eboraceus of the Hamilton group of New-York. 



GENUS FORBESIOCRINUS ( De Koninck). 

 y FORBESIOCRINUS COMMUNIS (n.s.). 



Body in the young state regularly turbinate, and becoming more 

 spreading in the older specimens. Basal plates sometimes visi- 

 ble as a thicker projecting rim more or less complete, at the 

 summit of the column : subradial plates small, subtriangular, 

 the lateral edges scarcely truncate. Primary radials four, wider 

 than high : secondary radials from four to seven, varying in 

 the different rays, smaller than the primary radials, and in 

 different proportionate strength in different individuals. Each 

 ray is usually three times divided, and rarely some one of the 

 divisions again bifurcates; while in some individuals the third 

 bifurcation is not complete. 



The interradial spaces in the older individuals are marked by the 

 presence of a single plate ; while in the young specimens, no 

 distinct plate, or but a granule, is visible. The first anal plate 

 is small, with two or three granules above it. The patelloid 

 plates of the rays, and their divisions, are distinctly visible 

 throughout all parts of the body. 



The column near its summit is composed of the thin joints cha- 

 racteristic of species of this genus, with longer and irregular 

 joints below, sometimes swollen in the middle, giving them au 

 annulated character. 



In this species, we have the characters of the lower part of the body seen in some 

 of the Carboniferous species of the age of the Keokuk limestone at Crawfordsville, 

 Indiana, where there are no interradial plates, and the anal area has but one distinct 

 plate. In those species the rays are continued above the first bifurcation, throwing 

 off lateral armlets, but not properly bifurcating. All the carboniferous species having 

 regularly bifurcating arms, as in this one, have interradial areas with numerous 

 plates. This species therefore combines in part the characters belonging to two 

 Carboniferous types of the genus, but possessing neither of them fully. 



A specimen from the Chemung group at Forestville, Chautauque county, New- 

 York, exhibits all the characters shown by this species, so far as they can be seen 

 in a single individual, one side of which is imbedded in the rock. 



