No. I.] THE METAMERISM OF NEPHELIS. 21 



serial sections, and permits a rapid glance at the order of 

 sequence of any character in different somites or individuals. 



Systematic. 



Nephelis differs from nearly all other leeches in the external 

 topography of the somite. While the somite in the Hirudinea, 

 as a group, is characterized by prominent sense organs on the 

 first ring, in Nephelis these are conspicuously absent, save on 

 a few segments near the anus and in rare instances on a few 

 rings near the mouth. The absence of these characters has 

 compelled investigators to resort to other criteria for the 

 determination of species, such as color markings, and the 

 occurrence of four stripes of pigment on the dorsal side is 

 sufficiently well marked to furnish a criterion of generic, if not 

 of specific, value. In Europe the only well-established species 

 is N. octoculaia Bergmann. Blanchard (4) says: "Jusqu'a 

 Savigny, la seule espece admise sans contest etait la N. octo- 

 ailata Bergmann : Savigny a distingue plusieurs esp^ces basees 

 exclusivement sur les differences de coloration : mais aucune de 

 ces esp^ces nominale n'est representee et n'est surement recon- 

 naisible. En outre de la N. atomaria, nous croyons pouvoir 

 separer de I'ancienne N. octocidata plusieurs autres formes 

 specifiques bien distinctes." 



Moquin-Tandon in the first edition of his monograph accepts 

 the description given by Carena for N. atomaria as a species, 

 but in the second edition lowers it to the rank of a variety of 

 N. octocidata. 



The first mention of the genus in this country that I have 

 found was made by Thomas Say (2) in 1824 under the name 

 of Hirudo lateralis, and this was changed by Verrill (3) in 1872 

 to N. lateralis. Leidy (5) described a forrii (1870) under the 

 name N. marmoraia. Verrill describes four species of Nephelis 

 found in the United States and says concerning three of them : 



' R. Blanchard : "Courtes notices sur les Hirudinees, III. Description de la 

 Nephelis atomaria Carena." Bull, de la Soc. Zool. de France, tome xvii, p. 165, 

 1S92. 



5 Jos. Leidy : " Description of Nephelis punctata." Proc. Acad. Nat. Sci. of 

 Philadelphia, p. 89, 1870. 



