ORTMANN: monograph of the naiades of PENNSYLVANIA. 319 



The nacre in all my specimens is silvery white, but is said to be sometimes more or 

 less reddish. Corresponding to the thinness of the shell, the hinge-teeth are deli- 

 cate, thin, and compressed. The sexual differences of the shell are similar to those 

 of L. cariosa. Beak-sculpture as described by Marshall (1890, fig. 7), and re- 

 sembling that of L. cariosa, but the median sinus of the bars is very indistinct or 

 even missing. I have only a single individual which shows the beak-sculpture. 



L. H. D. 



Size: 1. Newbold, Cat. No. 61.4012 (cf) 62 mm. 42 mm. 26 mm. 



2. do. " " do. (9) 46 " .30 " 20 " 



3. Plymouth, Cat. No. 01.667 (9) 38 " 29 " 18 " 



4. Princeton, Cat. No. 61.1.571 (sex?) .32 " 22 " 13 " 



This species grows somewhat larger, but the largest male given above is about 

 the average size. 



Soft parts and glochidia practically unknown. Lea (Obs. II, 1838, PL 15, 

 fig. 44) has given a poor figure of the soft parts of a gravid female, and an incom- 

 plete description (Obs. X, 1863, p. 455). 



Breeding season: Through Lea (Obs. II, 1838, p. 54) we know that this species 

 is gravid in autumn (October, November). Lea also reports (l. c., p. 57) a female 

 charged with eggs for June 5. Conner (1909) has confomided this species with L. 

 cariosa, and thus we cannot depend on his dates. 



Remarks: This species has been often misunderstood and confounded with L. 

 cariosa. In general terms it may be defined as a rather small and thin shell, with 

 dull-colored epidermis, and fine, indistinct, or missing rays, which, when present, 

 cover a larger part of the shell than is the case in L. cariosa. 



Localities represented in the Carnegie Museum: 



Plymouth, Plymouth Co., Massachusetts (Hartman collection). 



Delaware-Raritan Canal, Princeton, Mercer Co., New Jersey. 



Delaware River, Newbold, Gloucester Co., New Jersey (C. H. Conner) (received as L. cariosa). 



Lake Wacamaw, Columbus Co., North Carolina (G. H. Clapp, donor). 



Localities represented in the Philadelphia Academy. 



Ditches of Delaware Meadows, League Island, Pliiladelphia, Pa. 

 Delaware River, Westville, Gloucester Co., New Jersey (Morris Schick). 

 Delaware River, Kaighns Point, Camden, Camden Co., New Jersey (John Ford). 



Distribution and Ecology (See fig. 31): Type locality, Delaware River, Phila- 

 delphia (Say). 



According to Simpson (1900) this species is in the "Atlantic-drainage, from 

 New England to the Ogeechee River, Georgia," that is to say, it occupies about 



