Subfamilies, Genera, and Subgenera — Recent and Fossil 189 



The kidney (fig. 5) is rather short, about 1 mm. long and 0.3 mm. wide. 

 The ureter is very long and is folded back tightly against the lower part 

 of the kidney. A cross section near the middle of the kidney (fig. 6) shows 

 an oblong or ovate lumen with a small vein at each end. There is no super- 

 posed ridge. The kidney is wider than that of exacuous but narrower than 

 that of cooperi or c. callioglyptus. The pericardium is very wide. 



Digestive System. The digestive system is similar to that of exacuous 

 (see plate 48, figs. 4, 5). The radula sac is essentially the same as in 

 Menetus. 



The superior jaw (plate 50, fig. 9) of dilatatus is wide and low with 

 vertically striated face. The side jaws are as long as the width of the 

 superior jaw. The jaws of sampsoni (fig. 6) are similar, but larger. There 

 is a slight bulging in the center of the lower cutting edge of the superior 

 jaw in both dilatatus and sampsoni. 



The radula (plate 67, fig. 4, dilatatus). Center tooth squarish, not as 

 wide as in typical Menetus. Lateral teeth ( 1-7) squarish, tricuspid, the 

 mesocone longest, all cusps sharp and spade-shaped. Intermediate teeth 

 (8-10) becoming narrower and developing a split entocone and one or two 

 small cusps above the ectocone. Marginal teeth (11-14) long and narrow, 

 the entocone with three to four small subequal cusps, the ectocone with 

 several small cusps on the outer edge of the teeth. The marginal teeth 

 become much smaller toward the edge of the membrane. The radula of 

 sampsoni is practically of the same type as that of dilatatus (fig. 5). 



The material examined for anatomical data has been as follows: 

 dilatatus, near Unionville, Connecticut, twelve miles west of Hartford, col- 

 lected by F. C. Baker (16) ; near Hyannis, Cape Cod, ]\Iassachusetts, 

 collected by F. C. Baker (2) ; sampsoni, Merrimec River, near Stanton, 

 Franklin County, ^Missouri, collected by Mr. Leslie Hubricht (14) ; small 

 creek, six miles northeast of Dallas, Texas, collected by Dr. E. P. Cheatum 

 (4) ; slough, near Trinity River, twelve miles southeast of Dallas, Texas, 

 collected by Dr. Cheatum (2) ; small lake, near Hutchins, Dallas County, 

 Texas, collected by Dr. Cheatum (2). 



The cercariae or rediae of trematode worms were found in some of both 

 species of Micromenetus. Of dilatatus, near LTnionville, Connecticut, one 

 specimen infested; sampsoni, Merrimec River, Missouri, nearly all speci- 

 mens examined, many of the specimens being badly diseased. 



Geographical Distribution. The species belonging to the subgenus 

 Micromenetus are distributed over the eastern part of North America 

 from Massachusetts west to Iowa and Missouri, and from Maine and 

 ^Michigan southward to Alabama, Florida, and Texas. It is a group found 

 east of the Rocky Mountains. One species, Menetus uliginosus Vanatta. is 

 found in Bermuda. 



