438 H. Lyster Jaiuesou 



papilhie in intervak of larger ones. No ccjecum on beginning of 

 rectum. Nerve cord not mounted on a longitudinal muscular ridge. 



Now there are, in the genus Thalassema^ among the species 

 that have been described in such a manner as to be recognisable, 

 four species that agree with T. papillosum in haviag an undivided 

 longitudinal musculature, and only one pair of segmental organs. 

 Three of these, viz. T. gigas Max Müller (7), T. fcex Öelenka (9), 

 and T. lankesfcrl Herdman (4), differ from the species I am describiug 

 in the form of their anal vesicles, which are branched and tree-like 

 as in BoneUia. The fourth species, however, T. diaphanes Sluiter 

 (10), which inhabits the bay of Batavia, resembles T. jMpillosuvi in 

 the form of the anal vesicles. 



The general body form, the smaller size and the transparent 

 delicate skin of T. diapJ/ancs suffice to separate it from the Naples 

 species. 



At piesent the only members of the genus Thalassema known 

 from the Mediterranean are T. gigas, from Trieste, T. ncpiiuii re- 

 corded by Eietsch (8) from Marseilles, possibly however distinct from 

 the north European T. neptniii, the species recorded by Kowalevsky 

 from Messina ((>]. which has three pairs of segmental organs, and 

 the imperfectly described T. grolnnanm of Diesino it and 3) which 

 is quite too superficially described to be recognisable. It is there- 

 fore interesting to be al)lo to add even this imperfect account of 

 another member of this group from the Mediterranean. 



Zoological Station, Naples. 6i Dee. 1898. 



List of papers referred to. 



1. Delle Chiaje, S., Aniiuali invertebrati del Regno di Napoli. Vol. 3. 



Napoli 1841. pp. 118—119, 124 pi. 106 fig. 19. 



2. Diesing, K. M., Systema Helminthum. Voi. 2 1851 p. 74. 



3. Revision der Rhyngodeen. 1859 p. 57. 



4. II er dm an, W. A., Note on a new British Echiuroid Gephyrean. in: Q. 



Journ. Micr. Se. (2, Voi. 40 1897 pp. 367—384 pi. 27, 28. 



5. Jameson, H. Lyster, Contributions to the Anatomy and Histology of 



Thalassema neptuni, Gärtner, in: Z. Jahrb. Abth. Morph. 12. Bd. 

 1899 (not yet published). 



