ODHNER : ANATOMY OF SOME BRITISH PISIDIA. 



157 



the rear termination of th.e pedal slit proper is yet distinct ; its level 

 margins bend quite suddenly towards each other. The fissure 

 behind it has, on the contrary, uneven margins. This fissure certainly, 

 represents a branchial slit, the development of which has' been, 

 normally, suppressed in this species. 



Figs. 1-5. — Diagrams of the nephridia in a dorsal view of P. personatum (1), 



torquatum (2), clessini (3, 4), and amnicum (5). 

 Figs. 6-8. — Sketches of the left nephridium, seen from outside, of 



P. clessini (6), personatum (7), and nitidum (8). 

 Figs. 9-10. — Stomach and intestine, seen from the left, of P. clessini (9) 



and personatum (10). 



Nephridium. — As I have already mentioned in my paper of 1921, ■ 

 the nephridium of P. clessini shows a comparatively simple con- 

 struction. Text-fig. 6 gives a sketch of the left nephridium seen 

 from outside. The wall lining the pericardium {p), and that of 

 the most proximal portion of the nephridial canal, are more strongly 



