ORTMANN: monograph of the naiades of PENNSYLVANIA. 263 



about by a slight swelling and prominence of the lower margin in the postbasal 

 region, and in consequence of this the lower margin is straightcr in the middle, or 

 even slightly concave. The undulating character of the rays is generally more 

 pronounced in the female in the region of the postbasal swelling. On the average 

 the female shell also appears a little shorter and higher than the male shell. 



L 



Size: (Males) 1. Utica, Cat. No. 61.3377 37 mm. 



2. Sharpsville, Cat. No. 61.3378 32 



3. Utica, Cat. No. 61.3377 30 



4. Rosston' Cat. No. 61.2933 27 



(Females) 5. Walnut Bend, Cat. No. 61.3376 31 



6. Russell, Cat. No. 61.3375 29 



7. Sharpsville, Cat. No. 61.3378 28 



8. Russell, Cat. No. 61.3375 27 



The largest specimen in the Carnegie Museum is a male (without locality) 

 40 mm. long. 



Soft parts (See Ortmann, 1912, p. 339). Glochidia hitherto unknown, but I 

 have seen them in specimens collected in West Virginia. They are of the usual 

 shape, subspatulate, higher than long, but of rather small size. L. 0.17, H. 0.20 mm. 



Breeding season: Gravid females were found on May 13, 1911; May 23, 1911; 

 May 23, 1912. In every case glochidia were present. This agrees with the 

 assumption that the species is hradytictic. Nothing is known about the beginning 

 of the breeding season. 



Remarks: This species, and Toxolasma parvuni, are the smallest in our fauna, 

 and could not be possibly confounded with any others. The differences of these 

 two have been pointed out under Toxolasma parvum. Eurynia fabalis can be 

 easily recog-nized by the combination of a small shell with comparatively heavy 

 hinge teeth, and in this it also differs from the yoimg of other species, for instance 

 E. iris. It also has a certain resemblance to young Elliptio dilatatus, but the 

 latter is generally longer and thinner, has less hea\'3' teeth, more or less deeply 

 colored nacre, and not the peculiar rays seen in E. fabalis. 



I have only one specimen from Lake Erie (in Michigan): it is very small (13 

 mm. long), and has a rather bright green color. lean not teU whether there are 

 any striking differences from the normal type. 



Localities in Pennsylvania represented in the Carnegie Museum: 



Beaver River, Wampum, LawTence Co. (G. H. Clapp & H. H. Smith). 

 Mahoning River, Mahoningtown, Coverts and Edinburg, Lawrence Co. 

 Shenango River, Sharpsville, Mercer Co. 



