50 ILUNOIS BIOLOGICAL MONOGRAPHS [148 



In the largest specimen of this species, from the Sangamon River, the 

 right valve has a large blister parallel with the postero-ventral border, 

 measuring 17 by 7 mm., and anterior to this blister a group of twenty of 

 more 'pin-head' pearls. There are several of these small pearls in the center 

 of the valve. The left valve has a number of *pin-head' pearls bordering the 

 pallial line and one larger (1 mm.) black pearl in the center of the valve. 

 (Z11230 A). These may have been caused by distomid parasites, although 

 none were observed in the animals of this species. Onfy one shell in a dozen 

 were thus affected. 



28. Gminculma parva (Barnes). 



This diminutive mussel is characteristic of the smaller tributaries of 

 the Big Vermilion River. It occurs commonly in the ditch above Urbana 

 and also in Spoon River. No living specimens were found between the 

 Spoon River tributary and the station one mile above iron bridge north of 

 Sidney, a distance of over six miles. From this station to the railroad 

 bridge east of Sidney, a distance of three miles, this species was abundant 

 or common. It is infrequent at Homer Park and was not found in the 

 Salt Fork below Muncie or in Middle Fork. Its normal habitat in the Salt 

 Fork is on a mud bottom in quiet water. At Homer Park, however, it 

 occurs sparingly on a gravel bottom in very shallow water. 



The species as found in Salt Fork is normal in form but not of large 

 size, the largest specimen observed, from the railroad bridge east of Sidney, 

 measuring 30 mm. in length and 18 mm. in height (Z11096). The surface 

 in the Salt Fork specimens is rayless, the color being brown from the um- 

 bones to the center of the valve, the balance of the shell being black. 

 Specimens from Spoon River were smaller than those from farther down 

 the stream. 



Parva occurs infrequently in the Sangamon River at Mahomet on a 

 mud or sand bottom. 



29. Caruncullna glans (Lea). 



This small mussel, which is much higher in proportion to its length 

 than parva, is very rare in Salt Fork, where it was found at but three 

 stations, living individuals being collected only below the dam at Homer 

 Park. Like parva, it is a species of the smaller tributaries and its normal 

 habitat is on a mud bottom. It was not found in the Sangamon River at 

 any station examined. 



Frierson (1914: 7) has identified Lea's glans with the shell called 

 Unio (Toxolasma) lividus of Rafinesque, changing the generic, name, 

 accordingly, to Toxolasma Rafinesque. In this he is followed by Ortmann 

 (1918:572, 573). Should these names be plainly identifiable from the 

 original descriptions, these small shells will bear the names Toxolasma 

 parvutn (Barnes) and T. lividum Rafinesque. The writer wonders whether 



