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Show 1899.] WORMS PROM CHRISTMAS ISLAND. 55 ECHIUROIDEA. T H A L A S S E M A Gaertner. 1. T H . B A R O N I I Greef. Greef, SB. Ges. Naturw. Marburg, 4 July, 1872, p. 106; 4 May, 1877, p. 68 ; and Acta Ac. German, vol. xli. pt. ii. p.l." Selenka, Gephyrea,' Challenger' Report, vol. xiii. pt. xxxvi. P- L Fischer, Abh. Ver. Hamburg, vol. xiii. 1895, p. 1. A single specimen of this species represented the Echiurids in Mr. Andrews's collection. At first sight I took the animal to be an example of Fischer's species Th. pellucidum, which he remarks has certain resemblances with Th. baronii. It was about the same size a3 Fischer's examples, and the colour, which may have been altered by spirit, was similar to that of the young spirit examples of Th. pellucidum. Fischer states that in the older specimens the colour is bluish, and it is possible that the green tinge with its violet stripes which Greef describes in Th. baronii are only acquired with age. On the other hand, the specimen described by Selenka in the ' Challenger' Report from Bahia had lost its colour. There can be no doubt that this specimen was a young form; including the proboscis it was about 3 cm. long, whilst the adults of Greef attain four times this length. The structures on which I chiefly based m y identification were : (i) the two pairs of nephridia, found also in Th. formosulum and Th. exilii, where, however, there are eight bands of longitudinal muscles, and in Th. pellucidum, where there are thirteen; (ii) the form and shape of the " respiratory trees," which closely resemble those figured in Greef's monograph; (iii) the breaking up of the circular muscle-sheath into very fine and very numerous bands, clearly indicated by Greef in his fig. 64, plate vi.; and (iv) the number of longitudinal muscles, which is eighteen. This last point deserves some notice. In his systematic account of Th. baronii, Greef does not mention the number of strands of longitudinal muscle 5 indeed it was not until 1883 that Lampert drew attention to the importance of these structures in the determination of species. Greef, in. his figure of the species in question, indicates sixteen bundles, but as the cut edges of the skin are inflected it is reasonable to suppose that a further bundle has been hidden on each side. By some unexplained error, Lampert1 gives the number of longitudinal muscles as twenty-three; and this number has been copied by Rietsch into his ' Etude sur les Gephyriens armes ou Echiuriens '2. Fischer has recently re-investigated the original specimens of Greef and has found in them 18-19 muscles. Locality. Greef found his examples amongst the lava blocks and stones at low tide at Arrecife on Lanzarote, one of the Canary 1 Zeitschr. wiss. Zool. vol. xxxix. 1883, p. 334. 2 Geneva, 1886, or Recueil Zoologique Suisse, vol. iii. p. 505. |