162 AMERICAN JOURNAL 



breadth, both produced into acute points, the inner one twice as 

 long as the outer one, and more decidedly curved outward. 



Plate 12, fig. 1, gives a group of laterals such as we have now 

 described. These come from what appears to be the most de- 

 veloped portion of the membrane. As the membrane advances in 

 either direction from this point, the shape of the laterals is gradu- 

 ally modified, so that the above description will not apply to them. 

 At one extremity of the lingual membrane, the laterals appear 

 as figured in our fig. 4. From this it will be seen that the beak 

 of the recurved apex is divided into two stout, short, straight, 

 blunt points, instead of the sharply pointed, curving points de- 

 scribed above. 



At the opposite extremity of the lingual membrane we find 

 laterals in which the recurved apex is decidedly trifid, the three 

 divisions long, slender, acutely pointed, the central longest and 

 straight, the outer ones curving inwards. 



Besides the three prominent forms of laterals already de- 

 scribed, there are numerous modifications of each, the laterals 

 being very variable. 



The laterals pass gradually into the marginals, as shown in our 

 figure 5. The marginals are in obliquely curving rows. They are 

 short, narrow, rounded, with irregular bulging sides, recurved 

 into very long, rounded beaks, whose apices are bluntly bifid. 



LlMNiEA MEGASOMA. 



To Mr. Anthony also we are indebted for a specimen of this 

 species from Lake Ohamplain. In mounting the lingual mem- 

 brane a portion only was saved. From this we are able to give 

 only the form of the lateral teeth and the marginals. The laterals 

 (see fig. 6) are very much like those of Limncea appressa described 

 above. The recurved beak is, however, straighter, its larger 

 point being sometimes bifid. The marginals (see fig. 3) are more 

 widely separated, both in the rows and the individual teeth of 

 each row. They are also of more nearly equal size throughout their 

 length, have a longer recurved portion, and their apex is irregu- 

 larly digitate, rather than bifid, there being three and sometimes 

 four subdivisions. 



The jaws of Limncea megasoma are all shorter and stouter 

 than in L. appressa. 



Our figures are drawn from photographs taken directly from 

 the microscope by our friend, Mr. Sam. Powel. 



