INTRODUCTION. 
The present Report, unfortunately, does not fill up all the many deficiencies in his- 
tological detail left in my former Monograph on the genus Myzostoma. This is owing 
partly to the fact that the material at my disposal was not in a very first-rate condition 
for minute anatomical research, and partly to the small number of specimens of many of the 
species — sometimes only one or two — which, of course, prevented me from using them 
for histological investigation. Although this Report is on the whole chiefly systematic, 
it will, I hope, be found to further our knowledge of the group in the following respects : — 
1. It shows that the Myzostomida do not form such a uniform group as was 
formerly thought, either in structure or in mode of life. 
2. The numerous new species render more intelligible the structure and arrange- 
ment of the various organs of the body, which is of assistance in fixing the 
boundaries of species. 
3. Several of the new species throw considerable light upon the affinities of the group. 
In order to render this Report more complete, I shall give, in the description of species, 
a short account of all the species already known, but not contained in the collections 
that I have in my hands at present. 
The following is a brief account of the structure of Myzostoma, as far as it is known 
at present. 
The body (fig. 1) is a circular disk, provided along the margin with ten pairs of digitiform 
processes. On the ventral side, arranged in two semicircles, are five jDairs of non-articulate 
foot-stumps (parapodia), in the intervals between which, and nearer the margin, are four 
pairs of suckers ; at the end of each of the parapodia is a bent pointed hook supported by a 
straight rod, which in order to guide the hook is furnished at its extremity with a bent 
end-plate (manubrium) and several smaller hooks. The whole apparatus is capable of 
extension and retraction by means of a complicated system of muscles radiating outwards 
from a central ventrally placed muscular mass. Close to the anterior end of the ventral 
surface is the mouth, and close to the posterior end is the aperture of the cloaca. The 
alimentary canal consists of a muscular pharynx, which can be extruded through the 
mouth, of an oesophagus separated by a valve from the stomach, which is itself separated 
by a circular fold from the terminal portion of the canal — the rectum ; from the stomach 
a number of branched radiating caeca take their origin. Beneath the stomach is the large 
