378 C. O. WHITMAN. 
it has been carried one step further in L. acranulatum (fig. 
53). Here the 97th annulus represents the 97th and 98th (of 
L. pigrum and L. edentulum) fully consolidated as may be 
inferred from its size. We have thus only 104 annuli, with 
sometimes a trace of a 105th. These three species agree in 
having five abbreviated somites (embracing ten annuli) at the 
anterior end, and in the position of the genital orifices and 
nephridial pores. Their chief point of difference is the degree 
of abbreviation represented in the 97th and 98th annuli. 
5. Macrobdella sestertia,! nov. sp.—As the Macrob- 
della which I have examined differs in some important points 
from those described by Verrill, Leidy, and Brooks, I shall 
give a full description of the specific as well as the generic 
characters. 
Diagnostic Characters. 
Body has the shape and proportions of Hirudo of Europe, 
except that, anteriorly, it tapers rather more rapidly. The 
following measurements were taken from a _ middle-sized 
specimen: Length, swimming, 9°5 cm.; in extension, 13 cm. ; 
at rest, 5°38 cm. Width, swimming, 12 mm. 
Cephalic lobe, semi-ovate, smaller proportionally, than 
in-Hirudo; composed of four annuli. The thin margin is 
capable of considerable extension and is slightly emarginated 
at the tip; it is thickly beset with fine papille on its inferior 
surface. The under side of the cephalic lobe shows three con- 
vergent fossz, one median corresponding to the dorsal maxilla, 
and two lateral corresponding to the latero-ventral maxilla. 
When the Leech is at rest the head is usually rolled into the 
buccal cavity, as is the habit with all Hirudinide. 
Acetabulum circular and centrally attached; 6°5 mm. in 
diameter. 
Annuli 103; the last three very imperfectly marked. Most 
of the annuli appear to be double; but the two halves are 
separated by a comparatively shallow furrow. 
1 This name is given in allusion to the fact that the sexual openings are 
separated by two and a half rings, 
