ORTMANN: monograph of the naiades of PENNSYLVANIA. 87 



Marshall, 1895 (Allegheny River, Warren Co.). 

 Ortmann, 19096, p. 197. 



Characters of the shell: Shell small, or barely of medium size, but comparatively 

 heavy. Outline subtriangular to subovate, more or less elongated and dra^\^l out 

 posteriorly, very oblique, often cuneiform (high in front, tapering behind). Lower 

 margin convex or straight. Beaks not much elevated, moderately swollen, directed 

 obliquely forwards, and situated near the anterior end of the shell, sometimes 

 quite anterior. Beak-sculpture rudimentary^ indistinct, consisting of three to 

 four subconcentric ridges. Shell more or less swoUen anteriorly, less swollen and 

 more compressed posteriorly; sometimes with the anterior sweUing marked off quite 

 sharply from the posterior flat part, but hardly ever with a distinct radial depression. 

 In most cases the swollen anterior part passes insensibly into the compressed 

 posterior part. In some cases the shell is very little swoUen anteriorly, and the 

 valves are rather regularly and gently convex. No distinct posterior ridge. Sur- 

 face of shell smooth, without sculpture. 



Epidermis yellowish to light brown or pale chestnut, darker when old; gen- 

 erally with more or less distinctly green capillary rays, which are interrupted and 

 much broken, forming very often, and characteristically, squarish, or even trans- 

 verse green to blackish spots or blotches. Growth-rests not very different in color. 



Hinge well-developed. Pseudocardinals divergent, moderately large, ragged. 

 Interdentum not very wide, often rather narrow. Lateral teeth rather long. 

 Beak-cavity not deep. Dorsal muscle-scars on the hinge-plate. Nacre always 

 white. 



No sexual differences in the shell. 



L. H. D. 



Size: 1. Harbor Bridge, Cat. No. 61.3815 (largest) 78 mm. 51 mm. 36 mm. 



2. Eastbrook, Cat. No. 61.3335 74 " 45 " 27 " 



3. Eastbrook, Cat. No. 61.3335 64 " 40 " 23 " 



4. Eastbrook, Cat. No. 61.3335 54 " 35 " 2I " 



5. Mosgrove, Cat. No. 61.4328 39 " 29 " 19 " 



Soft parts (See Ortmann, 1912, p. 264, fig. 9). Glochidia (See Ortmann, 19116, 

 PI. 89, fig. 5). 



Breeding season: The following records are at hand for gravid females: :\Iay 

 22, 1912; May 23, 1911; May 23, 1912; May 24, 1911; June 18, 1908; June 27, 

 1910; July 8, 1909; July 8, 1911; July 10, 1908; July 19, 1909. Glochidia have 

 been found as early as June 18. Tachytictic form, breeding from about the middle 

 of May to the end of July. 



Remarks: A very distinct species, at least in Pennsylvania. It belono-s to 



