PLATE X\'. 

 Ptekixea flabella. 



Pnprc 93. 



Sec Plntos 14 mid SS. 

 Fiif. 1. An iiii|)ci-f'oit Icl't valve. 



Upper Heldei-liei-fi: lime-stone. Stafford, Gimtsee Ok, N. Y. 

 KifT. ■•. The internal moiilil of a siiiall left vahe, showing- the hing-e eharaetei-s and the museular 

 impressions. 



Hamilton g-ronp. Ol.icgo Co., N. Y. 

 Fiff. 5. The interior a.s obtained from an impression in g-utta-peroha. 

 Kiir. t). A left \alve, haviiijir tlie wing unusually large and extremely extended. 



Chemung group. Miuisfitld, Pa. 

 Fig, S. An enlargement of surface where the intermediate ra<lii ai'e nearly equal. 



Fig. 9. An enlargement of surface showing the alternating small radii, and strong, concentric 1am- 

 ellose striffi. 



Hamilton group. Skaneateles lake, N. T. 

 Fig. 10. An enlargement of a specimen preserved in calcareous shales, showing strong lamellae and very 

 unequal radii. 



Hamilton group. Hainhurg, Erie Co., N. Y. 

 The weathering of .«pecimcns like the one rejiresented in Fig. 10 often obliterate.s the finer 

 surface ornamentation, and leaves the lai-ger 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 tulevculata, with distant tuberculated ribs and interme- 

 diate strise. . . Ann. Rept. Geolog. Surv. N. Y., p. 117, 1838. This name should have 

 been cited in the sjTionomy of Avicula flabella, page 93 of this volume. 



Pterinea pinguis. 



Page 92. 

 See Plate 83. 

 Figs. 2, 3. Casts of two impei-fect left valves. The specimen fig. 2 is ro-drawn on plate 83, fig. 13, to show 

 the foi-m of the beak anil proportions of the valve. 



Upper Helderberg gronj). Near Columbus, Ohio. 



Pterinea dispanda. 



Page 97. 

 Fig. 7. The left valve described, showing the foi-m and surfaire charactei-s. 

 Chemung group. Mansfl^ld, Pa. 



Leiopteria Rafinesquii. 



PagelGl. 

 See Plates 20 and 88. 

 Kig. 11. A'left valve, slightly imperfect at the extremity of the wing. The auricle is siiniewhal tiKi much 

 Hxtended in the figure. 



I I iper Helderberg limestone. Dehncan: dliin. 



(tI.VPTODE.^MA occidentale. 



Page 157. 

 See Plate"86. 

 Kif;. 12. An inijierfect left valve. This specimen is better repi'esented on plate 8li, tig. H. 

 I'lijier Helderberg limestone. Fiitl.i of the Ohio. 



