PLATK LVIII. 



Gyroceras Eryx. 



Paso 386. 

 See Plate 103. 

 Fijr- 1. A septate fi-ag-menl of this ejiccies, sliowing the curvature of the tube and the depth of the air- 

 chaniliers. Fmni Doloinitic limestone, referred to the Hamilton group, near Milwaukee, Wis. 



Trochockrab Orjon. 



Page 397. 

 Fi},'. 2. Lateral view of a fragment, showing the curvature of the tube, the gibbous chamber of habitation 

 becoming straight, and contracting near the njierture. The sinus i-epi-esentcd on the doi-sal 

 side of the ajiertiire is incori-ect, and is not shown on the specimen. A broad sinus in the 

 ventral margin corresponds to the sinus of the surface-markings on the convex side of the tube. 

 Schoharie gi-it. Helderberg mountaiTis, N. Y. 



Trochoceras euqenium. 



Pat^ 396. 

 See Plate 59. 



Fig. 3. Lateral view of a small, coinpi-essed specimen, showing the curvature of the tube and the depth of 

 the air-chambei-s. Schohai-ie grit. /S'cAo*on>, i\r. Y. 



Fig. 4. A small, compressed, septate fragment, referi-ed to this species with doubt. The air-chambei-s are 

 shallower than is usual in the species, ami it may belong to the apical portion of ffyroeerat 

 tpinosum, but does not preserve any remains of the revolving rows of spines. The obliquity 

 of the septa and the slight deflection of the tube may be due to compression. 



Trochoceras obliquatcm. 



Page 401. 

 See Plate 111. 

 Fig. B. The concave dorsal side of a specimen, showing the transverse section of the tube and the want 

 of symmetry in the curvature. The view is looking upon the sjiecimen obli(juely, which 

 somewhat exaggerates the departure of the curvature from one plane. Schoharie grit. Scho- 

 harie, N. T. 



Trochoceras expansum. 



Tags 40>. 

 See Plate 111. 

 Fig. 6. The concave dorsal side of a compressed septate fragment, showing the depth of the air-chambers, 

 the curvature of the sutures, and the slight departure of the volution from pne plane. Scho- 

 harie grit. Scholiarie, N. Y. 



Trochoceras Pandion. 



Page 400. 



See Plate 111. 



Fig. 7. Lateral view of a fragment, showing the angular form of the tube, the depth of the air-chambers, 

 and the obliquity of the septa. Traces of the siphuncle are seen on the convex ventral side as 

 exposed in the process of weathei-ing. Schoharie grit. Schoharie, N. Y. 



Fig. 8. Lateral view of a specimen preserving about one volution, showing the curvature and form of the 

 shell. The apical portion is much compressed, and the evidences of the air-chambera oblit- 

 erated. Schoharie gi-it. Scholiarie, N. Y. 



Fig. 9. A septum of a fragment, showing the transverse section of the tube and the position of the siphun- 

 cle. Schoharie grit. Sclioharie, iV. F. 



