ECHIUROIDEA. 



By N. Ann and ale and Stanley Kemp. 



The Gephyrea are represented in the fauna of the Chilka Lake by a single Echiu- 

 roid belonging to the genus Thalassema, Gaertner. The species , which appears to 

 be undescribed, is of interest on account of its close relationship to T. sabinum, 

 Lanchester, from the Talé Sap in lower Siam (a lagoon that closely resembles the 

 Chilka Lake in many respects) and of the fact that a third closely related species 

 occurs in canals of brackish water on the outskirts of Calcutta. 



These three forms belong, in a sense, to the group typified by T. neptuni, Gaert- 

 ner (the type species of the genus) and characterized by the comparatively simple 

 nature of the anal trees, by the possession of two pairs of nephridia and by the undi- 

 vided sheath of longitudinal muscles. They have, however, certain very noteworthy 

 peculiarities — especially in the structure of the proboscis— that may ultimately be 

 considered to be of generic importance. The following key to the species of the 

 neptuni group, to which we assign provisionally those described here, may be 

 useful : — 



I. Proboscis long and slender, pointed or bifid at the tip, ex- 



tremely extensile, without dendritic or .finger-shaped out- 

 growths. 



A. Proboscis when expanded much longer than body, 



pointed . . . . . . . . T. neptuni, Gaertner. 



B. Proboscis when expanded not much longer than 



body, expanded and bifid at tip . . . . T. semoni, Fischer. 



II. Proboscis short and stout, truncate at tip, not very exten- 



sile, with dendritic or finger-shaped outgrowths. 



A. Proboscis tubular, (the lateral margins being fused 

 together), and containing internal finger-shaped 



outgrowths . . . . . . . . T. sabinum, Lanches- 



ter. 



B. Proboscis with the lateral margins not fused to- 

 gether, though capable of close apposition, bear- 

 ing dendritic marginal outgrowths. 



i. Dendritic outgrowths of proboscis small, 



less than half as long as it is wide . . T. dendrorhynchus, sp. 



nov. 



