Ix SYNOPSIS OF GENERA. 



1866. Geological Survey of Illinois, Palaeontology, vol. II, p. 334. Under 

 the discussion of Streblopteria, Mr. Meek states that " Prof. Winchell has 

 proposed the name Pemopeden* (Proc. Acad. Nat. Sci., Phila., July, 1865, 

 p. 125), for a somewhat similar type. That genus, however, diflfers in having 

 a central cartilage-pit under the beaks, with smaller pits along the hinge on 

 each side, while it wants the deep byssal sinus under the anterior ear of the 

 right valve, seen in Streblopteria." 



1868. Geological Survey of Illinois, vol. Ill, p. 453. Mr. Meek cites Pemo- 

 peden, Winchell (1865), with the species P. Shumardanus, Winchell ? pi. 14, 

 figs. 6a, b, and the following synonymy : 



" Avicula drculus, Hall, 1858, Geological Report Iowa, vol. 1, part ii, p. 522, 

 pi. vii, fig. 9. " Not A. drculiis, Shumard, 1855, Missouri Report, pi. C, fig. 14. 



"Pemopeden Skumardianus, Winchell, 1865, Proc. Acad. Nat. Sci., Phila., p. 126. 



"Compare A. Cooperensis, Shumard (1855), Missouri Report, pi. C, fig. 

 " 15 = ? Aviculopeden limaformis, White and Whitfield (1862), Proc. Bos- 

 " ton Soc. Nat. Hist., vol. viii, p. 295. 



1875. Geological Survey of Ohio, vol. 2, part ii. Palaeontology ; Mr. Meek 

 places Pemopeden Shumardanus, Winchell, under the genus EntoUum. See 

 citations under the latter genus. 



1877. Mr. S. A. Miller cites in his Catalogue the following species, viz. : 

 Pemopeden crenulatus, H., P. Jasdculaius, H., P. glaber, H., P. limiformis. White 

 and Whitfield, P. limatus, Winchell, P. obsoletus, H., P. Shumardanus, Winchell. 



From an investigation of the literature upon Pemopeden and EntoUum, and 

 a study of the type specimens of the former genus, it is evident that Pemo- 

 peden has priority and includes Peden demissus of Phillips. EntoUum, if existing 

 in nature, should be restricted to the species first indicated {E. aurarium), and 

 other allied forms, if any, and it is probably not found at all in the palaeozoic 



• "The type of Pernopecten is P. dmpereiui'ui — (AviclUa Cwrperrnsis, Shumard,— Avicnloi)ecten Ihna/onnis, 

 White anil Whitfield). The ty|)ical specimen of this species, figured by Dr. Sliuiuard in the Mis.souri Report, 

 shows a few oWure radiating' costic— an exceedingly rare cliuracter, tliougli we have occa.sionally seen 

 faint indications of them on other specimens. Hence, Dr. Shumard's species hiw not been generally identi- 

 6ed, and Prof. Hall, in the Iowa Keport, p. 52'2, pi. 7, fig. 9, erroneously refei-s apparently the same shell 

 to Avicula circulug, of Shumanl, a quite ditfcrent species." [Meek.] 



