PLATE XV. 

 Pterinea flabella. 



Page 



See Plates I I and 83. 

 Fig. I . An imperfect lefl valve. 



Upper Helderberg limestone. Stafford, ffenesa Co., .V. 1'. 

 Fig. I The internal mould of a Bmall lefl valve, showing the hinge characters and the muscular 

 impressions. 



Hamilton group. Otsego Co., N. Y. 

 Fig. .">. The interior as obtained from an impression in gutta-percha. 

 I ig 6. a lefl valve, having the wing unusually large and extremelj extended. 

 < Ihemung group. Mans/hid, Pa. 

 8. An enlargement of surface where the intermediate radii are nearly equal. 

 Pig. 9. An enlargement of surface showing the alternating small radii, and strung, concentric lam- 

 ellose stria. 



Hamilton group. Xkaneateles 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 lamella-, giving them a nodose character. A specimen in this condition was 

 described by Mr. Conrad as Avicula tuiereulata, with distant tuberculated ribs and interme- 

 diate stria'. Ann. Kept. Geolog. Surv. N. Y., p. 117, 1838. This name should have 

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



Pterinea pinguis. 



Page 92. 

 See Plate 83. 

 IV-. l'. :'.. < lasts of two imperfect left valves. The specimen fig. 2 is re-drawn on plate 83, fig. 13, to shew 

 the form of the beak and proportions of the valve. 



Upper Helderberg group. Near Columbus, Ohio. 



Pterinea dispanda. 



Page 97. 

 Fiir. 7. The left valve described, showing the form and surface characters. 

 Chemung group. Mansfield, Pa. 



Leiopteria Kafinesquii. 



Page 161. 

 Si-,- Plates 20 and 88. 



]•],, ]] A'left valve, slighth imperfect at tl xtremitj of the wing. The auricle is somewhat too much 



extended in the figure. 



Upper Helderberg limestone, Delaware, Ohio. 



(il,\ PTODESM \ OCCIDENTALE. 



Page i"'T. 



See Plate 86. 



Kit;. 12. Aii imperfect left valve. This specimen is better represented on plate 86, fig. St. 

 Upper Helderberg limestone. FullsoftJu Ohio. 



