PLATE XV. 
Pterinea flabella. 
Page 93. 
See Plates 14 and 83. 
Fig-. 1. An imperfect left valve. 
Upper Helderberg- limestone. Stafford, Genesee Co., N. Y. 
Fig. 4. The internal mould of a small left valve, showing J;he hinge characters and the muscular 
impressions. 
Hamilton group. Otsego Co., N- Y. 
Fig. 5. The interior as obtained from an impression in gutta-percha. 
Fig. 6. A left valve, having the wing unusually larg-e and extremely extended. 
Chemung group. Mansfield, Pa. 
Fig, 8. An enlargement of surface where the intermediate radii are nearly equal. 
Fig. 9. An enlargement of surface showing the alternating small radii, and strong, concentric lam- 
ellose strise. 
Hamilton group. Skaneateles lake, N. Y. 
Fig. 10. An enlargement of a specimen preserved in calcareous shales, showing strong lamellae and very 
unequal radii. 
Hamilton group. Hamburg, Erie Co., N. Y. 
The weathering of specimens like the one represented in Fig. 10 often obliterates the finer 
surface 'ornamentation, and leaves the larger rays with transverse ridges marking the place 
of the stronger lamellae, giving them a nodose character. A specimen in this condition was 
described by Mr. Conrad as Avicula tuberculata, with distant tuberculated ribs and interme¬ 
diate striae. . . Ann. Rept. Geolog. Surv. N. Y., p. 117, 1838. This name should have 
been cited in the synonomy of Avicula flabella, page 93 of this volume. 
Pterinea pinguis. 
Page 92. 
See Plate 83. 
Figs. 2, 3. Casts of two imperfect left valves. The specimen fig. 2 is re-drawn on plate 83, fig. 13, to show 
the form of the beak and proportions of the valve. 
Upper Helderberg group. Near Columbus, Ohio. 
Pterinea dispanda. 
Page 97. 
Fig. 7. The left_valve described, showing the form and surface characters. 
Chemung group. Mansfield, Pa. 
Leiopteria Eafinesquii. 
Page 161. 
See Plates 20 and 88. 
Fig. 11. A'left valve, slightly imperfect at the extremity of the wing. The auricle is somewhat too much 
extended in the figure. ^ 
Upper Helderberg limestone. Delaware, Ohio. 
Glyptodesma occidentale. 
Page 157. 
See Plate'86. 
Fig. 12. An imperfect left valve. This specimen is better represented on plate 86, fig. 9. 
Upper Helderberg limestone. Falls of the Ohio. 
