MOORE: HIRUDINEA OF SOUTHERN PATAGONIA. 677 



stant relation to the bands of circular muscles. Each primary annulus 

 possesses five of these bands, between the second and third of which the 

 furrow passes on ai and between the third and fourth on 0.2 and <zj. 

 VII aj is somewhat swollen at the mid-dorsal line, where also the furrow 

 VII/VIII may become obliterated for a short distance owing to the 

 development of the nuchal gland on the succeeding somite. The nuchal 

 plate may sometimes slightly overlap VII aj, or the latter may be some- 

 what constricted mesially by the glandular swelling. In some examples 

 the cross-furrows are not visible on VII and they are always less distinct 

 than on the larger annuli of VIII and succeeding somites. 



VIII is chiefly remarkable from the presence of the nuchal gland. This 

 is confined to az, which, as a consequence, is swollen and more or less 

 elongated in the median dorsal region. The horny plate secreted by the 

 gland, which it covers like a scale, is remarkably thick and conspicuous. 

 In color it has a very dark brown center and a paler border. Unlike G. 

 stagnalis it is broader than long, anteriorly very convex, posteriorly slightly 

 convex or straight. It slightly overlaps or just reaches VIII #<? and just 

 reaches the furrow VII/VIII anteriorly. But little change is noticeable 

 in the character of the somites to XXIII inclusive, though the secondary 

 furrows are frequently more distinct on the somites immediately succeed- 

 ing the region of the genital pores. 



On XXIV, which remains triannulate, the secondary furrow is present 

 on ai only and even there has become less distinct. On the ventral side 

 the annuli of this somite are crowded together by the posterior sucker. 

 XXV is biannulate and of much reduced length. The first annulus is 

 about one half larger than the second and about equal to the contiguous 

 annulus of XXIV. XXVI is faintly biannulate, aj being very narrow 

 and indistinct. XXVII is uniannulate and is cut into two halves by the 

 anus, which thus lies just posterior to XXVI (Plate L, figs. 19, 20 

 and 21). 



Pigmentation. From many of the specimens the pigment had faded 

 altogether, but all of those in which this is not the case show a very evi- 

 dent metameric arrangement, resulting in many cases in a strongly annu- 

 lar pattern, which is dependent on the disposition of the muscles. In a 

 typical example (Plate L, fig. 17) the ground color is a faintly mottled, very 

 pale brown, which deepens on the margins and fades to a gray on the ven- 

 tral surface. Dorsally, two broad, ill-defined, longitudinal bands extend 



