1899.] WORMS FEOM CHRISTMAS ISLAKD. 55 



ECHItJROIDEA. 



Thalassbma Gaertner. 

 1. Th. BAROiv'ii 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. 1.' 

 Selenka, Gephyrea, ' Challenger ' Eeport, 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. haronii. It was about the same 

 size as Fischer's examples, aud 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. haronii 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 pi-oboscis it was about 3 cm. long, whilst the adults 

 of Greef attain four times this length. 



The structures on which I chiefly based my 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 2^h. 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, 

 cleai'ly 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. haronii, 

 Greef does not mention the number of strands of longitudinal 

 muscle ; indeed it was not until 1883 that Lain pert drew attention 

 to the importance of these structures in the determiuation 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, Lampert ^ gives the 

 number of longitudinal muscles as twenty-three ; and this number 

 has been copied by Eietsch into his ' Etude sur les Gephyriens 

 armes ou Echiuriens ' '. 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 



^ Zeitschr. wiss. Zool. vol. xxxix. 1883, p. 334. 



^ Geneva, 1886, or Recueil Zoologic[ue Suisse, vol. iii. p. 505. 



