PROCEEDINGS OF THE MALACOLOGICAL SOCIEXY. 121 



ORDINARY MEETING. 



Fkiday, 8th May, 1908. 



B. B. WooDWAnD, F.L.S., President, in the Chair. 



Professor G. C. Bourne and Mr. H. 0. N. Shaw were elected 

 members of the Society. 



The following communications were read : — 



1. "On the Radulse of the British Helicids." By Rev. E. W. 

 Bowell, M.A. 



2. " Fossil Pearl-growths." By R. Bullen Kewton, F.G.S. 



3. "Description of a new species of Batissa from the Fiji Islands." 

 By H. B. Preston, F.Z.S. 



4. "jS'otes on Planorhis and its subdivisions." By Dr. W. H. Dall. 



Mr. G. B. Sowerby exhibited the unique specimen of Co7ius excelsus, 

 since acquired by the British Museum. 



The President exhibited specimens, both recent and fossil, of 

 Pisidium fersonatum, Malm. 



Dr. W. G. Ridewood exhibited specimens of separated cerata or 

 dorsal processes of two species of Nudibranch Mollusca, either Tethys 

 or Melibe, from Ceylon and Japan. The Ceylon specimens were three 

 in number, and were sent by Mr. James Hornell, Marine Biologist to 

 the Government of Ceylon, and Inspector of Pearl Banks; the Japan 

 specimens were three in number, and were collected by Mr. R. Gordon 

 Smith, who described them as smelling strongly of eucalyptus when 

 caught. Both were obtained by the trawl, and both exhibited lively 

 movements for some considerable time after capture, and responded 

 fairly readily to mechanical irritation. The Ceylon specimens were 

 1^ inches long and 1 inch wide ; the Japan specimens measured 

 3 inches by 2J. 



Dr. Ridewood reviewed the literature bearing upon the subject, 

 and pointed out that in the first reference to such bodies, by Cavolini 

 in 1785, they were identified as the gills of a Tethjs. Renier, how- 

 ever, in 1807, took them to be external parasites on the Tethys, and 

 called them Hydatula varia. Rudolphi (1817) also regarded them as 

 parasites, and named them Phcenicurus varius, and Otto (1823) 

 adopted the same view and named them Vertummis tethydicola. 

 Delle Chiaje, again, in 1823, described the bodies as Planarian 

 Worms parasitic upon Tethys, and he explained the regularity in 

 their arrangement in paired series along the body as due to the fact 

 that they attached themselves by their mouths to the nipple-like 

 projections that occur in two regular rows along the back of the 

 Tethys, each in the middle of a gill. 



Macri (1825), on the other hand, agreed with Cavolini in regarding 

 the structures as gills or similar organs of the Tethys, and he divided 

 the genus according to the number and arrangement of these organs. 

 Verany (1840) and Krohn (1842) also regarded the bodies as parts 

 of the Tethys, and Dujardin (18'15), in his treatise on Worms, refused 



VOL. VIII. — OCTOBER, 190S. 11 



