76 
THE VOYAGE OF H.M.S. CHALLENGER. 
Stelechopus, n. gen. 
The body is flat and long, the month at the anterior margin, the cloaca at the 
posterior; alimentary canal with no ramified caeca. Five parapodia on each side on the 
margin of the ventral surface, each one of which contains a fine long hook, and a support- 
ing seta. The parapodia are entirely independent of each other, the parapodial muscles 
being very simple, and the radial musculi centrales, connected in the genus Myzostoma with 
a central muscular mass, are here absent. Instead of the radial muscular bundles (septa), 
there are numerous parallel muscular bundles joining the intestine to the body- wall. 
Suckers are wanting. 
68. Stelechopus hyocrini, n. sp. (PI. XVI. figs. 1-7). 
The principal features in the organisation of this, the only species of Stelechopus, are 
stated in the generic definition. It appears to be undoubtedly the lowest form of 
Myzostomida, and ought therefore to decide the question concerning the affinities of the 
group with certain lowly organised Arthropoda (Tardigrada, Linguatulida). This affinity 
was formerly brought forward by me (Genus Myzostoma, p. 71), and I there proposed to 
unite the three groups into a single Class — Stelechopoda. It is therefore greatly to be 
regretted that the only specimens (nine individuals mounted in Canada balsam by 
v. Willemoes Suhm) which I received from Mr. Murray in November 1882, do not 
permit of an accurate study of the anatomy of this form. Any one having at his 
disposal abundant fresh material could undoubtedly render a great service to science. 
Fig. 1 is a drawing which shows all that could be made out from all the different 
specimens ; it is a combination figure. The specimen, however, from which the 
contour was drawn had been greatly squeezed, and the figure therefore does not give 
a right idea of the external form, and must be supplemented by a comparison with 
figs. 2-4. 
The body when extended has a general similarity to a Tardigrade ; the lateral margins 
are nearly parallel, and become somewhat narrowed at either end of the body. The 
anterior extremity is sometimes conical in form and highly prominent (fig. 1), sometimes 
retracted, and then looking as if truncated; the posterior extremity always projects as 
a conical caudal appendage ( CA ) between the last pair of parapodia. The largest speci- 
men measured 3 '5 mm. long with a greatest diameter of ‘9 mm., the smallest was 1 mm. 
long and '34 mm. broad. The caudal appendage of the former had a length of - 07 mm., 
of the latter '06 mm. The body is flattened, and covered by a chitinous cuticle, reach- 
ing a thickness here and there of '006 mm. in the largest specimen, highly refracting and 
yellowish in colour. Towards the mouth and cloaca, and at the end of the parapodia 
