16 Proceedings of Royal Society of Edinburgh. [sess. 
The body is elongated, more markedly attenuated posteriorly than 
anteriorly. The colour is brown. At the head end there is a 
shallow mouth cavity, and besides this on the lateral line at each 
side a very prominent papilla ; somewhat further back there is 
another weakly developed. No transverse wrinkling of the cuticle 
is to be observed. The musculature is very strongly developed, 
and is referable to the Holomyarian type. 
The male measures on an average 1 6 mm. in length by 4 mm. 
in breadth, and is much attenuated posteriorly. The oesophagus is 
short, and occupies only °f th© total length. The tail has a 
spoon-shaped termination, which is supported by three finger-shaped 
processes (fig. 2). The two laterals each bear three papillae, the 
median two ; and in front of the cloaca on each side there is another 
papilla with a finger-shaped stalk. The two cirri are 0*84 mm. 
in length. A bursa, with rolled margin (fig. 4), occurs on lateral 
edges of the tail in the male forms. Among the longitudinal muscles 
there are strong oblique bursal muscles, which extend very far for- 
ward, for 3-2 mm. There is a remarkable longitudinal strand, which 
consists of shining spherules, and lies in the ventral line in the plane 
of the longitudinal muscles, whence it gives off lateral branches at 
right angles to right and left (fig. 4). 
The female measures 16 ‘5 mm. in length by 4*8 mm. in breadth. 
It is viviparous. The unpaired short vagina and the long paired 
uteri opening into it are filled with very numerous embryos. These 
measure 0*36 mm. in length by 0*013 mm. in breadth. The oeso- 
phagus occupies % ifar of the total length, and is therefore very short. 
Close in front of the apex of the tail, which divides into two roundish 
processes, lies the anus (figs. 5 and 6, b). In front of this one 
notices an oval vesicular elevation of the cuticle, in the middle of 
which the vulva appears in the form of a transverse slit (figs. 5 and 
6, a). It is bordered anteriorly by a slight protrusion of the 
parenchyma of the body, posteriorly by a similar thicker structure 
(fig. 6). 
The six known species of Pseudalius appear to flourish where 
there is an abundant supply of oxygen, since they live in air- 
containing organs or in the blood- vascular system. 
Ps. alatus, in the pharyngeal cavities, mouth, and Eustachian 
tube of Monodon monoceros. 
