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 circularl}^, and from this layer there pass up the longi- 

 tudinal fibres of the fore wall of the collar (fig. 14, ifiv.). 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 ca?lom into the collar — the peri- 

 lipemal and peripharyngeal spaces — are related essentially as in 

 the known species of Ptychodera. As in Pt. sarniensis and aperta, 

 the perihfemal spaces, with the exception of their anterior portions 

 which are situated entirely below the collar cord (fig. 16, pits.), 

 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, w^iich 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 filjres. 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, p2^s.), while ventro-laterally it terminates along the point 

 of origin of the circular vessel fold, 



CoUa7' Cmlom : 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, eve). Ventrally a longitudinal space exists, into which 

 the ventral vessel fold projects, and on the dorsal side, just 



