40 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
Length, fully extended, 25 mm.; partially contracted (as in Figure 27), 
about 10 mm, 
Width, fully extended, less than 1 mm.; partially contracted (as in Figure 
27), about 1.5 mm. 
Color. — The anterior and marginal parts of the body are very clear and 
transparent. The rest of the body is usually of a pale yellowish-white color 
when the animals are first collected, but changes to a rusty yellow or pale 
orange color if they are kept in well-lighted aquaria for a few days. The color 
is due to the presence in the deeper parts of the body of rounded reserve-food 
cells, similar to those described as occurring in G. stagnalis. Apparently the 
nature of the granules in the reserve-food cells changes under the influence of 
daylight, so that by reflected light they appear pale orange instead of yellowish- 
white, the color which they have when first collected. 
Superficial pigment cells of the branched type, described as occurring in G. 
stagnalis and other species, appear to be entirely wanting in G. elongata. 
Fat cells occur in abundance in the deeper parts of the body, the contained 
oil drops being perfectly clear and transparent, as in G. stagnalis and G. fusca. 
6. Rinxes, Somites, Eyes, Suckers. 
The skin is very smooth and entirely free from papille. 
External rings, broad and smooth, usually indistinct in the head region 
(somites I.-Iv., Figure 23). Number of rings, 62 between oral sucker and anus 
(somites V.—XXVII.). 
Notwithstanding the indistinctness of the rings in the head region, favorable 
preparations, like that represented in Figure 6, show that the composition of 
somites I.-Iv. is practically the same in this species as in G. heteroclita (Plate 5) 
and G. fusca (Plate 4). Somites I. and I. are uniannulate; somites 111. and 
tv. biannulate, the anterior rings being broader and corresponding to rings 1 and 
2 of a typical somite taken together. 
Somite v. is likewise biannulate in this species, just as in G. stagnalis 
(Figure B; compare Plate 1, Figure 3) ; in all the other species with which 
this paper deals, somite v. is triannulate. 
Somites v1.-xx1v. (Figure 27) are triannulate, as in all other known species 
of this genus. Somites xxvy.-xxvil. are reduced each to a single ring, a con- 
dition found in the other species described only in the case of somite XXvVIZ., 
somite xxv. being always biannulate, and somite xxv. usually so. 
Eyes, two, situated about as in G. stagnalis, just posterior to the mouth, 
between somites 11. and Iv. (Figure 23). The eyes are separated from each 
other by a considerable space, as in G. stagnalis (Plate 2, Figure 4) and G. fusca 
(Plate 4, Figure 16). The pigment associated with them is usually small in 
amount; often it is wanting altogether. 
The oral sucker, as in the other species described, lies within the limits of 
somites 1.-Iv. The mouth lies about in its centre (Figure 23, Plate 6; Figure B). 
The posterior sucker (act., Figures 24, 27) is extremely small and weak. In 
