ENTEROPNEU8TA HILL. 345 



Round the terminal portion of the body there is below the 

 limiting membrane of the epidermis a thin layer of circular 

 muscles which, with the delicate circular muscles round the 

 terminal part of the intestine, form a sphincter round the anus. 



SUMMARY. 



(1) The Pacific species, P. hedleyi, is to be associated with the 

 two European species P. minuta and P. sarniensis in the sub- 

 genus Ptychodera (sensu stricto), especially characterised by the 

 rudimentary character of the genital pleura. 



(2) In the possession of a continuous axial canal in the dorsal 

 nerve cord, opening both anteriorly and posteriorly, P. hedleyi 

 agrees with P. sarniensis, while in the possession of two longi- 

 tudinal epidermal stripes overlying the two ciliated grooves of 

 the intestine, it agrees with P. australiensis. 



(3) P. hedleyi exhibits affinities with the members of the sub- 

 genus Chlamydothorax (P. erythrcea, P. bahamensis, and P.flava) 

 in the possession of a dorsal thick-walled glandular division of 

 the intestine just behind the branchial region. It is suggested 

 that this dorsal diverticulum may, in P. hedleyi, have some diges- 

 tive function. 



(4) As regards the degree of development of the dorso-ventral 

 muscle plate, P. hedleyi may be best compared with Balanoglossus 

 kupfferi. 



(5) P. hedleyi differs from all hitherto described species of the 

 genus Ptychodera, and agrees with the members of the genus 

 Balanoglossus in the absence of a circular musculature in the 

 trunk. 



REFERENCE LETTERS. 



an. Anterior neuropore. 



av. Afferent vessels of subepidermic capillaries of proboscis. 

 bps. Body of proboscis skeleton. 

 brg. Branchial groove. 

 cbs. Central blood-space of proboscis. 

 ccl. Collar canal. 



ccp. Prolongations of collar coelom into the proboscis neck. 

 cfw. Circular musculature of outer wall of anterior rim of collar. 



ch. "Chondroid tissue." 



cl. Cleft into which dorsal vessel opens, 

 cm. Circular musculature of proboscis. 

 cnc. Collar nerve cord, 

 cnl. Axial canal of collar nerve cord. 



COK. Collar crelom. 



cce'. Part of collar coelom into which the collar canal opens. 

 div. "Notochord." 



