1 6 Cincinnati Society of Natural History. 



figure A, Plate I, tiie plates varying Init little in form and size. 

 This ridge begins at the liasal curvature and continues upon the 

 edge of the dorsal side until the fourth plate, where it begins to 

 leave the edge, and more so in the fifth; and in the sixth plate 

 begins to take its regular course upon the specimen, approaching 

 nearer the edge towards the upper extremity; it has a position uj)- 

 on the specimen about one-fourth of the entire width from the 

 dorsal or straight side. The ridge is low in the basal curvature, 

 and is highest in the center, still being very strong at the upper ex- 

 tremity. The plates in the basal curvature are so arranged as to 

 make a very rapid, short curvature, forming a semi-circle and end- 

 ing bluntly. (This may have been a point of attachment.) In the 

 center the plates are the widest and gradually decrease in width 

 towards the upper extremity, thus forming a long curvature from 

 the fifth plate to upper extremity. 



As the ridge has the position above mentioned, it thus leaves 

 a very short rapid slope on the dorsal side, and a long slope on the 

 other or ventral side, this slope being about three times as long as 

 the other, with a general depression in the center of the slope. 

 Each plate having a rather marked depression beginning at the 

 ridge and top and slo])ing to the end of each plate. This depres- 

 sion has a position to the ridge of about thirty degrees, being strong 

 in the central plates and very faint or wanting towards the upper 

 extremity. I consider Plate No. I of Hall and Whitfield's J'liii/iiil- 

 itcs Jai/iesi, figured in Ohio Pal. Vol. II., as one of these plates 

 broken away from the ridge. The authors have thus been misled 

 in describing it as triangular in form, and this form is very charac 

 teristic of the plates in the genus Plinniilitcs or Turrilcpis. Fig. D, 

 Plate I, is an entire plate of this series, which has a position above 

 the basal curvature, and if it were one of the basal curvature 

 plates, it would have the slope towards the dorsal side, curved 

 more towards the under part of the ridge, which, as before stated, 

 causes the ridge to be on the edge of the basal curvature. This 

 can be seen in figure A, plates i, 2 and 3, having the slope entirely 

 under the ridge ; and in ])late 4 this slope begins to show, and 

 more so in the fifth, and in the sixth plate the slope shows its full 

 length. 



The opposite long row of plates or flat row, has fourteen to 

 fifteen overlapping plates, as shown in Figure B, with a very strong 

 general depression in the center of the specimen, above the basal 

 curvature to the upper extremity. This row of plates makes a 



