THK NAUTILUS. 117 



Species : tuherculata Raf. 



3. Genus : Pleurohema (Raf.) Ag. (enlarged). Outer gills serv- 



ing as marsupium. Supra-anal separated i'rom the 



anal. 

 Species: cooperiana (Lea)* — cBSojo«<s (Green). 



ohliqua (Lam.) [including the form pyramidata 



(Lea) and the var. coccinea (Conr.).'' 

 clava (Lam.). 



4. Genus : Unio Retz.* 



Species: crassidens (Lum.^—gibbosvs (Barn.) — cowplanatus 

 {J)\\\v{.)—productus (Conr.) (Fulton Co., Pa.). 



3. Subfamily : Anodontin^, 



Water-tubes similar to those of the Uniomnce, only less regular at 

 base of gills, chiefly so in the male. Supra-anal opening well sep- 

 arated from the anal ; sometimes the connection of tlie mantle mar- 

 gins is very long. Diaphragm normal. Inner lamina of inner gills 

 generally free from the abdominal sac, sometimes with the tendency 

 to become connected with it, or entirely connected. No papilla; on 

 mantle edge in front of branchial opening. Marsupium formed by 

 the outer gills; edge of marsuphim, when charged, distending, the 

 thickened tissue forming the edge stretching out in a direction trans- 

 versal to the gills, but not bulging out beyond the edge of the gill (or 

 only slightly so). Water-tubes in the gravid female divided longi- 

 tudinally into three tubes, one lying toward each face of the gill, the 

 third in the middle ; only the latter contains eggs or embryos, and 

 is much larger than the outer tubes. This division into three parts 

 is not present in the sterile female. Glochidia subtriangular, with 

 one spine at the tip. 



1. Genus: Alasmidonta Say.* 



^Pleurohema cooperiana (Lea) (= Qu. cooperiana of Simpson) surely groups 

 with PI. xsopus. 



^ PL obliqua, pyramidata [and also joZfna (Lea)] form a natural group by 

 themselves, and probably are one and the same species. P. pyraviidata is only 

 an extreme variation of P. ohliqua., with which it occurs, while coccinea is a 

 good ecological variety, which, however, runs into ohliqua at certain localities. 



3 The characters of the soft parts of Unio are practically identical with those 

 of Pleurohema. A distinction is possible only by shell characters. 



*The genera of the Anodontinx are distinguished chiefly by shell characters, 

 but it seems as if Alasmidonta and Slrophilus are more closely allied to each 

 other, and then again Symphy7ioia, Anodontoides and Anodonia. 



