2 MEMOIRS OF THl CARNEGIE MUSEUM. 



such forms as are not found in Pennsylvania, has been secured and studied. This 

 made necessary a number of changes, which chiefly affect the division into genera, 

 and which have been published (Ortmann, 1912). The system proposed in this 

 latter paper will be used in the following pages with such corrections as have 

 become inevitable in the course of still further studies. 



With regard to the systematic literature, I have refrained from giving a full 

 list of references and synonyms under each species, since the citations given by 

 Simpson (1914) are as complete as could be desired. The quotation of the earlier 

 reports from Pennsylvania was deemed desirable, in order to get an idea of the 

 advance made in recent years in our knowledge of the subject. 



Family MARGARITANID^ Ortmann (1911). 

 Ortmann, 1911a, p. 129; 19116, p. 334; 1912, p. 223. 



Genus Margaritana Schumacher (1817). 

 Ortmann, 1912, p. 230; Simpson, 1914, p. 511. 



Type My a margaritifera Linnaeus. 



1. Margaritana margaritifera (Linnseus) (1758). 



Margaritana margaritifera (Linn^us) Simpson, 1914, p. 513. 



Plate I, fig. 1. 

 Records from Pennsylvania: 



Lea, Obs. II, 18.38, p. .56, and VII, 1860, p. 225. As to the correctnefss of these records, see below. 

 Hartman & Michener, 1874, p. 91. See also below. 

 Conner, 1904, p. 91 (Still Creek, Quakake). 

 Ortmann, 19096, p. 208. 



Characters of shell: Shell large and heavy, cyhndric-ovate, elongate, often 

 arcuate when old. Anterior end rounded, posterior produced. Beaks very little 

 elevated. Epidermis blackish or blackish brown. Nacre whitish, pinkish, or 

 somewhat purplish, posteriorly iridescent. Pseudocardinal teeth present, laterals 

 obsolete, generally entirely wanting. Inside of the mantle-line a number of small 

 muscle-scars. • 



Size: My largest specimen (from Rene Mont) measures: L. 152 mm.; H. 67 

 mm.; greatest D. 49 mm. This is larger than any of the previous records. The 

 m?iximum length given by Carl (1910, p. 65) for the form found in the Odenwald, 

 Germany, is 136 mm. Israel (1910, P- 177) gives 140 mm. for the form from the 

 Elster-drainage in Germany. 



OEC 10 1938 



