58 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



the abbreviated shape of the whole tooth. The tooth which follows 

 may be regarded as transitional or first marginal with equal propriety ; 

 it is furnished with a very slight prominence marking the place of an 

 endocone. There are 13 to 16 marginals, closely set, with very curved 

 basal plates ; their cusps are of average length, and do not overlap the 

 next row to any great extent. 



The specimen here figured was extracted by me from one of the 

 original specimens from Solothurn, now in Mr. Kennard's collection. 

 My warmest thanks are due to him for permitting the somewhat risky 

 operation of extraction to be performed on so valuable a specimen. 

 The proximal parts of the genitalia, showing an extremely short vas 

 deferens, commencing two-thirds of the way down the sheath of the 

 male organ, and a shoe -shaped spermatheca with a short, stout, and 

 twisted duct, are shown at Fig. 5 of the accompanying illustrations. 



Mr. B. B. Woodward, with his invariable kindness, has permitted 

 me to make a careful examination of the specimen (radula) of 

 V. helvetica which he described in 1903, when he showed that the 

 English specimens referred to helvetica could not well be that species, 

 and therefore gave them the name of Roger si ^ in honoiir of the original 

 British discoverer. It has been remarked by several students of the 

 group that the specimen figured by Woodward seemed to be abnormal, 

 in respect of possessing a first admedian without separated endocone. 

 That was the conclusion I myself had formed from an examination of 

 the figure. When Mr. Woodward first showed me the specimen, some 

 months ago, I had to admit that the peculiarity occurred with such 

 regularity, on both sides of the radula, that it might be a normal 

 feature. On that occasion it was examined with a Zeiss D objective. 

 After that came the preparation of the companion radula, from the 

 shell in Mr. Kennard's collection ; and this is very markedly normal ; 

 i.e., it has the type of admedian to which we are accustomed in this 

 group of VitrecB. I then made a number of preparations of Vitrece, 

 fixing the radula together with its natural investments, taking 

 pai'ticular care not to remove the cells which coat the upper surface 

 of the unused part, but to fix them with as little shrinkage as possible. 

 These preparations show that the rounded cavity between the endocone 

 and mesocone is normally filled up by a group of cells which seem to 

 act as a plug to prevent the advance of chitinisation in that cavity, 

 while the other surfaces of the cusps continue to become thickened 

 till the middle of the organ is reached. On closely examining 

 Mr. Woodward's helvetica radula with apochromatic objectives of 

 unexceptionable definition, I soon came to the conclusion that the 

 only material difference between it and Mr. Kennard's specimen was 

 that this group of cells had itself become impacted and chitinised in 

 the cavity. I have since found several other instances of the same 

 kind of thing ; it may be described as a very slight pathological 

 abnormality. Abnormalities arising from fusion of basal plates are 

 not rare in this group, but they rarely occur on both sides of the 

 radula symmetrically. A group of teeth from Mr. Woodward's 

 specimen is here figured (Fig. 3) ; the emphasising of the endocone 

 of the transitional tooth figured is not a constant character throughout. 



