224 Annals of the Carnegie Museum. 



This family is divided into three subfamilies, as follows: 



I. Subfamily Unionin.e Ortmann. 

 Rarely no supra-anal opening formed, it is generally. present, sep- 

 arated from the anal opening by a shorter or moderately long mantle- 

 connection. Marsupium formed by all four gills or by the two outer 

 ones, when charged, only moderately swollen, and its edge not dis- 

 tending. No secondary water-tubes developed within the marsupium. 

 Glochidia rather small, or of medium size, subovate, without hooks; 

 or subtriangular, with hooks. 



2. Subfamily Anodontin.e Ortmann. 

 Supra-anal opening always well separated from the anal opening, 



often by a very long mantle-connection. Marsupium formed only 

 by the two outer gills, when charged, greatly swollen, and an extra 

 thickness of tissue at the edge permitting the gills to distend. Within 

 the marsupial gill, the water-tubes are divided during the breeding 

 season into two lateral (secondary) water-tubes lying toward each 

 face of the gill, and a central ovisac, which is closed at the base of the 

 marsupium. Glochidia rather large, subtriangular, with hooks. 



3. Subfamily Lampsilin.e Ortmann. 



Supra-anal opening always separated from the anal opening by a 

 mantle-connection of medium length, rarely entirely closed. Mar- 

 supium formed by the two outer gills, or by parts of the latter, gener- 

 ally situated in their posterior portion. When charged, the marsupium 

 extends beyond the original edge of the gill, an extra thickness of 

 tissue at the edge permitting a bulging out. Water-tubes of mar- 

 supium not subdivided, when charged. Often special structures 

 (papilla? or flaps) on the edge of the mantle, chiefly of the female, in 

 front of the branchial opening. Glochidia of various sizes and shapes, 

 small to rather large, either subovate, without hooks, or celt-shaped, 

 with two spines on each valve. 



Family III. Mutelid.e Gray (emended). 2 

 Diaphragm complete, formed anteriorly by the gills, posteriorly by 

 a firm union of the margins of the mantle. Anterior end of inner gills 



2 As has been stated in a previous publication (Ortmann, 1911a), the nomencla- 

 ture of this family and its subfamilies is only provisional, until additional genera 

 (chiefly Mutela itself) have been investigated. 



