4 ON A NEW SPECIES OF ENTEROPNEUSTA, 



this is found the t3^j)ical ring furrow forming the fourth region 

 [figs. 1 and 15 (4)], and this is separated from the trunk by a 

 narrow projecting circular rim— the fifth region — which forms the 

 posterior boundary of the collar, and is somew^hat wider than the 

 succeeding trunk section. The collar may reach a length of 

 9 mm. with a transverse breadth in the third region of 9 mm. 

 also, so that in the living animal the collar may l)e said to be 

 aliout as broad as long, but in preserved specimens the transverse 

 breadth, owing to the strong contraction of the longitudinal collar 

 musculature, considerably exceeds the length, and also the ventral 

 length slightly exceeds the dorsal. 



Trunk. 



( 1 ) Branchio genital Region; This region may reach a length 

 of from 36 to 40 mm. and a breadth of 7 mm. PL australiensis 

 is especially characterised by the great development of the genital 

 wings — the duplications of the dorso-lateral regions of the body in 

 which the gonads are situated — and in this respect the species is 

 to be associated with Pt. aperta, clavigera, gigas, and aurantiaca, 

 in Spengel's provisional genus Tauroglossus. The anterior ends 

 of the wings are continuous with the posterior rim of the collar, 

 and immediately behind the latter their free edges may either 

 slightly overlap each other or they may be infolded, and the wings 

 then are in contact in the median line by their outer surfaces. 

 The wings continue posteriorly in this condition and reach their 

 maximum size somewhat posterior to the gill region. This con- 

 dition is retained, in a slightly varying degree in different 

 individuals, to within a short distance of the most anterior 

 liver sacs, which are more or less completely hidden from view by 

 the wings. Beyond this point the wings decrease raj^idly in size 

 and form two ridges lying at first laterally to the liver sacs but 

 which are finally covered by the outer overhanging ends of the 

 laro-er liver sacs (fig. 24, gw.), and which disappear altogether in 

 the posterior part of the hepatic region. 



When the wings have the position just described no part of 

 the gill area is visible externally, and the most anterior small liver 



