BNTEROPNEUSTA HILL. 207 



Proboscis. The proboscis of this species, like that of the 

 P. minuta and P. sarniensis, is relatively short. It has a greatest 

 length of 9 mm., and a breadth of 5 mm., i.e., its length is not 

 quite double its breadth. In form it is somewhat egg-shaped, or 

 more accurately, its outline may be compared with that of the 

 human tongue. A distinct median sulcus is present, on its dorsal 

 surface, in some specimens, but not in all, and may simply be due 

 to contraction in preservation. 



Collar. The collar appears about as broad as long, with a 

 greatest length and breadth each of 5 mm. It is considerably 

 shorter than the proboscis, in the proportions of 5 : 9 and 4 : 7 

 in two individuals. 



The five regions of the collar are distinct, and in their relations 

 are characteristic for the species. The first region includes the 

 anterior free part of the collar, and occupies about a third of its 

 entire extent. Its free margin is slightly crinkled, but is not 

 markedly expanded frill-like, as in P. australiensis* This free 

 part of the collar narrows posteriorly, and passes over into the 

 second region, occupying the middle third of the collar. 



This second region appears of a darker colour than the first, 

 and is somewhat broader than the latter. It forms a distinct 

 circular cushion, narrowing anteriorly where it joins the first, and 

 broader posteriorly where it adjoins the third region. The 

 posterior third of the collar, constituting its broadest portion, 

 includes the third, fourth, and fifth regions. 



The third and fifth regions are formed by two prominent 

 circular ridges of about equal size, and are separated from each 

 other by a circular groove constituting the fourth region. The 

 circular rim of the fifth region forms the posterior margin of the 

 collar, and has a distinctly greater transverse diameter than the 

 succeeding branchio-genital section of the trunk, so that the 

 collar appears distinctly marked off from the latter. 



In the specimens the collar shows distinct longitudinal grooves, 

 no doubt produced by the contraction of the collar musculature. 



TRUNK. 



(1.) Branchio-genital Region. This region is characterised by 

 the great length of the branchial area, and the absence of genital 

 pleura, the latter however being represented in the genital region 

 proper by genital cushions (cf. infra). 



It may be subdivided into a branchio-genital region, co-exten- 

 sive with the gill area, and into an exclusively genital region 

 behind the point of termination of the gills. In the largest 



* J. P. Hill On a New Species of Enteropneusta (P. australiensis), 

 from the Coast of New South Wales. Proc. Linn. Soc., N.S.W. (2), x., 

 1894. 



