42 PERCY SLADEN TRUST EXPEDITION 
Localities. Three specimens “from fallen and decaying leaf-base of palm in very 
damp place, 1500 feet, Silhouette Island, Seychelles,” the fourth specimen “from a 
Pandanus leaf-base, above Mare aux Cochons, Silhouette.” 
Several issues, not wanting in interest, are raised by the discovery of Idiobdella 
seychellensis. 










































XIV — XX 













Tdiobdella seychellensis. Diagram of (A) dorsal and (B) part of ventral surface, showing eyes, annulation 
and external openings. Somites numbered in Roman, and rings in ordinary figures. n.p., nephridiopores ; 
an., anus. 
In the absence of any evidence supporting the view that this species and the other 
members of its Series are survivors of a type more primitive than that possessing three 
jaws, we may assume, with more than a fair share of probability, that the Duognathoferee 
are derived from some form not far removed from Hamadipsa, and are led to enquire by 
what means the loss of the supero-median jaw was brought about. 
The Gnathobdellide present a fairly complete series of forms ranging from typical 
