DIBOTHEIA FROM YELLOWSTONE NATIONAL PARK. 
73 
breadth was 3 millimeters ; the thickness about 1.25 millimeters. The posterior ex- 
tremity of this sj)ecimeu was truncate and slightly emarginate, and about 2 millimeters 
broad. Anteriorly the body is somewhat tapering, rather cylindrical, and extremely 
irregular in outline. The body is crossed by tine transverse strim which appear to be 
incipient joints. Towards the posterior and larger end these strim become more dis- 
tinct and therefore the body there assumes a decidedly segmented appearance. 
Anatomy. — The following remarks on the anatomy and the sketches are based on 
sections of portions stained in toto in borax carmine. 
Musculature . — The musculature is very similar to that of L. eatostorni. 
The layers of the body from without inward are, first a cnticnlar layer ; next a 
layer of longitudinal and radial fibers with much granulo-nuclear protoplasm inter- 
spersed ; next a vascular layer in which the peripheral system of aquiferous vessels is 
well represented along with many nuclei and, in the autero-mediau and median parts of 
the body, numerous calcareous bodies. This layer merges into a granulo-nuclear layer 
within, and is succeeded next by a prominent layer of longitudinal muscles. The lat- 
ter is separated from the inner core by a narrow layer of circular or transverse mus- 
cles. No definite system of muscle fibers was made out in the inner core in median 
section; anteriorly the arrangement is like that of L. eatostorni. The parenchyma 
there shows an irregular net-work of connective fibers, with numerous nuclei and im- 
mense numbers of calcareous bodies interspersed. In the near vicinity of the margi- 
nal canals and around the aquiferous vessels nuclei are very abundant. Sections of 
the anterior end show the presence of the two oiiposite bothrial pits, characteristic of 
the genus Dibotlirmm (plate XXV, tig. 2, e). 
Vascular system. — This, with the exception of a feature to be mentioned i)resently, 
appears to be much like that of L. eatostorni. In sections of the anterior end several 
small vessels were observed in the peripheral region. These became even more promi- 
nent in sections farther back. 
The marginal canals soon make their ajipearance. As in L. eatostorni, they are larger 
than the central aquiferous vessels, do not have a distinct wall, and the lumen, instead 
of being open, is tilled with jiale, unstained, spongy connective tissue, appearing some- 
what fibrous in longitudinal sections. They are densely surrounded by nuclei. Near 
the anterior end the transverse section of one was .05 by .03 millimeter in its two 
diameters. A few sections of the head were characterized by a distinct line of nuclei 
connecting the two marginal canals (idate XXV, tig. 2, d). The marginal canals retain 
their distinctive character to the posterior end. In longitudinal sections they are seen 
to pursue a gently undulating course. 
The aquiferous vessels of the inner core appear in sections near the anterior end as 
two i)rincipal vessels which lie near the central border of the marginal canals. As in 
L. eatostorni, these vessels have a distinct wall and an oiien lumen. One of these ves- 
sels, in the same section from which the diameters of the marginal canal given above 
were obtained, measured .019 millimeter in its outer and .011 millimeter in its inner 
diameter. The walls of the aquiferous vessels are quite distinct from the surrounding 
tissue and present on the outer surface, in cross-sections, a peculiar roughened appear- 
ance, as if thickly beset with minute bristles. The inner surface of the wall appears 
smooth in cross-sections. In longitudinal sections made in the i)ostero-median regions 
of the body the aquiferous vessels were seen to iiursue a somewhat tortuous course, 
and their folded and crumpled walls cut through looked like a series of frills or ruffles. 
