20 
ON A NEW SPECIES OF ENTEROPNEUSTA, 
surface of the collar cord. Anterior to the circular vessel fold 
there occurs a fairly thick band of muscle fibres which arise from 
the sides of the proboscis skeleton, and surround the mouth 
aperture circularly, and from this layer there pass up the longi- 
tudinal fibres of the fore wall of the collar (fig. 14, ifw.). The 
radial fibres passing between the fore and outer walls of the 
anterior margin of the collar have the usual intercrossing arrange- 
ment (fig. 14, rf.). 
The extensions of the trunk coelom into the collar — the peri- 
hsemal and peripharyngeal spaces — are related essentially as in 
the known species of Ptychodera. As in Pt. sarniensis and aperta, 
the perihernial spaces, with the exception of their anterior portions 
which are situated entirely below the collar cord (fig. 16, phs.), 
enclose between them a groove in which the ventral two-thirds of 
the collar cord is situated (figs. 17 and 18, phs.). The greater 
portion of their cavities is occupied by the longitudinal muscu- 
lature of the dorsal wall, which is inserted anteriorly in greater 
part into the boundary membrane of the epidermis behind the 
proboscis canal. On the ventral wall of each space there is a 
single layer of longitudinal fibres, while between dorsal and 
ventral walls there pass radial fibres. The peripharyngeal space 
(figs. 17, 18, pps.) is related exactly as in Pt. minuta. As in that 
species, there pass across the circular fibres which it contains 
numerous connecting strands between its inner and outer limiting 
membranes. Anteriorly it terminates on the dorsal side about on 
a level with the opening of the notochordal lumen into the throat 
(fig. 14, pps.), while ventro-laterally it terminates along the point 
of origin of the circular vessel fold. 
Collar Ccelom : In the anterior part of the collar the spongy 
connective tissue containing radial muscle fibres fills up the coelom 
almost completely, but posteriorly where the fibres are arranged 
in the form of radial strands there remain between adjacent 
strands spaces free from connective tissue just as in Pt. minuta 
(fig. 18, cw ). Ventrally a longitudinal space exists, into which 
the ventral vessel fold projects, and on the dorsal side, just 
