SYNOPSIS OF GENERA. 



Ivn 



APPENDIX. 



Observations upon the genus Pernopecten, and allied genera* 

 PERNOPECTEN, Winchell. 



Pi-oc. Acad. Nat. Sci. Philadelphia, p. 125. 1865. 



[Tyi>e Aviculopecten Hmifonnis, White and 'Whitaeld.] 



In part EntoUum, Mbbk. Geol. Siii-v. California, vol. i, p. 479. 1865. 



"Generic Characters. — Shell bivalve, sub-equivalve, monomyary. Valves 

 more or less inequilateral and auriculate. Hinge-line straight; hinge furnished 

 with a central, triangular cartilage-pit, and a transverse plate bearing on each 

 side of the middle, a series of smaller pits, diminishing in size and depth from 

 the centre outward. The shell seems to be thin, and probably has a structure 

 more like Peden than Perna." 



Fig. 1. Pkrsopbctbn limifoumis. A view of the type specimen of the species and of the genus 

 Burlington sandstone. Burlingttm, Iowa. 



Fig. 3. An enlargement to two diameters of the cardinal portion of the preceding as obtained from a 

 gutta-jienha impi-ession, showing more clearly the chai-actei-s of the hinge. 



Fig 3. PBRNorEOTBN Shumardanus. An enlargement of the cardinal portion of one of the type speci- 

 mens of this species, showing the charactere of the hinge. Waverly group. Newark, Ohio. 



* These observations were written in 1884 to accompany a general descnption and discussion of the 

 PalsBozoic Monomyaria, and fomied a part of the original plan for the introduction to the present volume. 

 The discu.ssions of the genera of the Monomyana have been deferred for the present, but as the genus 

 Pernopecten hau been recognized in the Report of the State Geologist for 1882, and also refei-red to in note, 

 p. 81, Pal. N. Y., vol. v., pt. 1, Lamellibranchiata, 1, it is necessary to introduce here the portion treating 

 of Pernopecten and allied forms. 



