98 The Irish Naturalist. i^iay, 



matters in order to invite further research ; but certainly this 

 curious phenomenon of phallic decrescence in a well-known 

 form like Vitrina seems worthy of special notice. It may 

 assist us to estimate what at first sight seems to be discrepant 

 evidence given b}' several distinguished anatomists concerning 

 the construction of Geomalacus. I ought also to mention that 

 in one specimen of V. pyrenaica (the largest of the ten) the 

 intromittent organ was found turned upwards in the direction 

 of the vagina ; on careful observation I was unable to satisfy 

 myself that the appearance was artefact. 



The maxilla is figured at J ; the size and direction of the 

 striae is as shown. There is no indication of bilateral origin. 

 The actual length (width) of this object is 0*6 mm. The radula 

 is shown in the remaining figures (Iv, M, N). The basal plates 

 are foot-vShaped in the larger marginals, graduall)^ becoming 

 rhomboid towards the outer edge , even those under the 

 centrals and laterals are distinguished for the concavity of 

 their sides. This is indeed a generic characteristic. But the 

 greater number of laterals, greater length of mesocones, 

 presence of distinct endocones on laterals,^ great shortening 

 of the ectocones of the marginals (so that the marginals no 

 longer have the shape of a little hand with fingers together 

 and thumb erect b}* itself, as in V. pelliicida), and the absence 

 of external serration to the marginals ; all these points com- 

 bine to make the radula easil}^ recognisable. The scale of 

 figures L, M, and N, can be ascertained by reference o the 

 micrometer divisions (each representing 10 /z, ten micra) traced 

 below them. 



In conclusion, I must tender my heartiest thanks to Messrs. 

 A. S. Kennard, P. H. Grierson, and R. A. Phillips, whose 

 kind assistance has provided me with the material described 

 above. 



Pensliurst, Kent. 



^ I have a Herefordshire Vitrina radula ^iiich shows these distinctl}', 

 and has marginals not nnich unlike those of K pyrenaica. Specimens of 

 V. pelhicida that I have taken in the South of Kngland show no variation 

 in these matters. The Herefordshire form just mentioned is, however, 

 distinctly not V.pyrcnaua. 



