8 PROF. E. R. LANKESTER ON THE CARDIAC [Jail. 16. 



just above the suture, and a line of spots in the pale interval on the 

 last whorl; spire attenuate; suture well impressed; whorls 7, 

 sides well rounded ; aperture ovate ; the ridge in the centre of the 

 columellar margin. The basal portion of a previous aperture may 

 be noticed occasionally in young specimens of Melania. 

 Size: — 



Major diain. 1*6, alt. apert. I "3, alt. axis 4-0 millim. 

 „ „ 006, „ 0-05, „ 0-16 inch. 



EXPLANATION OF THE PLATES. 

 Plate I. 



Figs. 1, 1 «, \h. Planorbis exustus, var. maculatus, p. 3. 



2, 2 a, '2 b. coclcburnii, n. sp., p. 4. 



3, 3(1, 3 J, 3 e. Planorbis socotrensis, n. sp., p. 3. 



4, 5. Hydrobia (?) balfouri, n. sp., p. 4. 



Plate II. 



Figs. 1, 1 a, 2, 3. Melania scabra, pp. 5, 6. 



4, 5, 6. tuberculata, p. 5. 



7, 8. sclatcri, p. 7. 



9, 10. • fagocla, pp. 6, 7. 



11. amarula, p. 7. 



2. On the Right Cardiac Valve of Echidna and of Ornitho- 

 rhynchus. By E. Ray Lankestek, M.A., E.R.S.j Jodrell 

 Professor of Zoology in University College^ London. 



[Eeceived January 14, 1883.] 



(Plates III. & IV.) 



Since I had the honour of placing before the Society the results 

 obtained by the examination of the hearts of two specimens of 

 Ornithorhynchus m last June (Proc. Zool. Soc. 1882, p. 549), I 

 have been enabled by the kindness of friends to extend my obser- 

 vations upon the structure of the right cardiac valve in the Mono- 

 tremata. On the one hand, Professor Flower has very kindly allowed 

 me to examine the hearts of two specimens of Echidna aus- 

 tralis belonging to the museum of the Royal College of Surgeons ; 

 and on the other hand, the late Professor Frank Balfour placed in 

 my hands six specimens of Ornithorhynchus paradoxus preserved in 

 spirit, whilst an additional specimen of the heart of Ornithorhynchus 

 (making nine in all) was communicated to me by Dr. Pye Smith. 



Additional Specimens of Ornithorhynchus-^ea/'^s. — In my former 

 paper it was shown that the right cardiac valve differed considerably 

 in the i\yo Ornithorhynchus-he&xti, then described; and it was inferred, 

 from the descriptions given by those authors, that the hearts examined 

 respectively by Owen and by Gegenbaur differed in respect of their 

 right cardiac valve from either of the hearts examined by me. 



Heart No. 1 of my tormer paper presented, besides a large anterior 



