382 Mr. H. N. Moseley on Pelagonemertes. 



Postscript. Hince the above was written, my attention has 

 been directed by Dr. von Willemoes-Suhm to Lesson's original 

 figure of Pterosoma in the ' Zoology of the Voyage of the 

 Coquille' (which work we have been able to consult, with a 

 splendid series of similar publications, in the Hawaian Govern- 

 ment Library at Honolulu), and to the many points of re- 

 semblance between Pterosoma and Pelagonemertes. 



Pterosoma plana is described by M. Lesson, l Voyage de 

 la Coquille, Zoologie,' Paris 1830, p. 254, and figured, pi. iii. 

 figs. 3 and 3 bis. 



Pterosoma was obtained in great abundance by Lesson be- 

 tween the Moluccas and New Guinea, August 31st, 1828. 



The animals measured 3 inches and some lines in length, 

 18 lines in breadth, and 3 to 4 lines in thickness. In general 

 form and gelatinous structure Pterosoma resembles closely 

 Pelagonemertes j further in that a series of polygonal areas are 

 marked out on its surface. The spirally-wound organ de- 

 scribed as a tube, which is indicated in the figure of Ptero- 

 soma^ can scarcely be any thing else than the proboscis of a 

 Nemertine — the mouth, at the extreme end of the body, being 

 probably the aperture of the proboscis-sac, and the fusiform 

 nucleus the sac itself. On the other hand, it is difficult to con- 

 ceive that Lesson, with a number of specimens available for 

 examination, could have missed seeing the very conspicuously 

 burnt-sienna-coloured ramified intestine of Pelagonemertes , had 

 such been present in his Pterosoma. Further, in Pterosoma 

 a pair of elongate, closely opposed eyes are described and 

 figured, having transparent coloured cornese. 



On the whole, now that a pelagic Nemertine is known to 

 exist, there seems little doubt that the animal seen and figured 

 by Lesson was a Nemertine and not a mollusk ; but it seems 

 to have been a distinct form, with a pair of eyes and an un- 

 branched digestive tract. 



EXPLANATION OF PLATE XI. 



Representing various structures occurring in a young specimen of 

 Pelagonemertes Rollestoni. 



Fig. 1. Pelagonemertes Rollestoni, enlarged, viewed from the dorsal 

 surface ; the prohoscis is partly extruded. P, proboscis ; Pr.S, 

 sac of proboscis ; I. P, invaginated portion of proboscis within 

 the proboscis-sac ; G, superior nerve-ganglion ; N.C, nerve-cords ; 

 V, vascular trunk (the upper V points to an enlargement of the 

 vessel lying just posteriorly to the superior nerve-ganglion) ; 

 I, intestine; D, diverticula of intestine ; 0,0, ovaries; CM, 

 circular muscles ; L.M, longitudinal muscles. 



Fig. 2. One of the ovaries, enlarged. The dark irregular line on the 

 centre represents what is probably an aperture for the discharge 

 of ova. 



