52 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
XXVI. are commonly divided at the margin of the body into a broad anterior 
and a narrow posterior portion. Somites mI. and Iv. are biannulate, the broad 
anterior ring in each case bearing the sensille and representing both the an- 
terior and the middle ring of a triannulate somite (Figure 2, I11.-vI.). The 
remaining preanal somites (v.-xxIv., Figure 6) are triannulate, but the pos- 
terior annulus of xxiv. is narrower than the adjacent annuli (Figure 6), and 
the anterior and middle annuli of somite v. are united ventrally while sepa- 
rated by only a very shallow furrow dorsally (7, 8, Figures 2, 36, Plate 1. 
These two cases illustrate the centripetal progress of abbreviation (or arrested 
development), that part of each terminal triannulate somite being affected 
which is adjacent to an abbreviated somite. 
In Figure 32, Plate 8, is shown a rather unusual condition, the apparent 
disappearance of the furrow separating somites 11. and 111.4 
The total number of preanal rings is sixty-nine, counting somites I., IL, 
and XXV.-XXVII. as uniannulate, 111. and Iv. as biannulate, and V.—xxXIV. as 
triannulate (Figure 6). 
ec. Eyrs, MoutH, Ora Sucker. 
The eyes appear in the living animal, or in whole preparations, as a single 
pair closely united and situated in rings 3 and 4 (somite 111.). See Figure 6, 
Plate 1; and Figures 32, 33, Plate 8. An examination of sections, however, 
particularly of young individuals, shows that there are really three distinct 
pairs of eyes present, there being a small rudimentary pair anterior, and an- 
other still more rudimentary posterior to the principal pair of eyes, exactly as 
shown for “C. hollensis” by Whitman (92, Figure 6). 
All three pairs of eyes? are partially imbedded in a common pigment mass, 
the anterior and middle pairs being directed forward, the posterior pair back- 
ward, just as in G. elegans and G. heteroclita (Figures 20, 29). The largest 
1 A similar condition is figured by Whitman (’91*) in his Plate 15, Figure 1S ie 
his text, however, Whitman says (p. 412): ‘In front of the eyes I was unable to 
discover any distinct rings. In another species C. chelydre, from Wisconsin, there 
are three narrow rings in front of the eyes; and the first is marked by the usual 
metameric sense-organs. Although no metameric sense-organs were recognized 
in front of the eyes in C. plana, the correspondence of other metameric characters 
in the two species is sufficiently close to enable me to identify the ocular rings as 
equivalents. The preocular part of the head is, therefore, probably equivalent to 
the first somite of C. chelydre, and is so numbered in Figure 1.” 
In view of Whitman’s subsequently published studies on “ The metamerism of 
Clepsine ” (92), I think he unquestionably would now recognize two preocular 
somites both in “ C. plana” and in “C. chelydra ”; at any rate, that is the number 
found in the species which I am describing (Figure 2, Plate 1). Since Whitman 
has pointed out no other difference between his “plana” and “chelydre ” than 
the uncertain one of preocular rings, I consider that their specific distinctness 
remains to be established. 
2 Only the largest (middle) pair of eyes appear in the section shown in Figure 2. 
