TOMLIK ANiJ BOWELL : VERTIGO MOULlNSlANA. 2I5 



two are definitely rejected by W. G. Binney on the ground of differences 

 in dentition {Terr. Air-Breathing Moll. U.S.A., vol. 5, pp. 215, 218), 

 but Sphyradiuin edeniulum has replaced V. simplex on the U.S.A. list 

 (cf. Nautilus, vol. II, p. 142). The other two have not been accepted, 

 and, judging by the material at our disposal, seem improbable. V. 

 ventricosa Morse is a small highly-polished species, if mm. x i^ mm., 

 with five denticles coloured as the shell, and an aperture shaped 

 differently to that of V. moulinsiana Dup. Dr. Bottger, in " Die 

 Entwicklung der Ptipa-Arten des Mittelrheifigebietes,^'^ considers the 

 two forms identical. Binney^ states that he had not seen either 

 V. ventricosa or its radula, and he quotes from Morse and gives 

 Morse's figures. As to the number of teeth, he states that there 

 are thirteen on each side of the central, and of these he regards 

 the first six as laterals. In examples of V. moulinsiana from 

 Cambridgeshire and from Co. Carlow, there are from twenty-two to 

 twenty-six teeth on each side of the central ; there is no difficulty in 

 counting them under an objective of medium power. The first nine 

 or ten of these might be regarded as laterals, but all the teeth are 

 really of the same type, and it would be better to speak of laterals 

 only in those cases where {e.g.) aculeate and quadrate teeth occur on 

 the same radula. The teeth before us are all tricuspid, the cusps 

 being shaped like little spearheads, so that each tooth presents the 

 appearance of a capital E (without serifs) lying on its back. The 

 middle cusp is always the shortest. Besides these three cusps there 

 is a varying number — from two to five — of accessory cusps at the base 

 of the larger ones. These were at first regarded as an optical illusion, 

 but careful examination shows them to be actual cusps. As in 

 Punctum and Succinea, the individual tooth has somewhat the shape 

 of a ladle, and the form of the basal plate is very characteristic. 

 Binney's figure of V. ventricosa shows short rounded denticles instead 

 of spear-like cusps, and even those disappear altogether on the mar- 

 ginals. He speaks of them, however, on p. 214 as " each bearing (I 

 presume) a distinct cutting point." There is no doubt that the best 

 microscope available in 1878 (the date of his work above cited) would 

 have failed to show the points of these cusps. From the figure there 

 is every reason to suppose that Morse's species possesses teeth of 

 the same character as our moulinsiana, but they appear to be 

 decidedly less numerous, and to diminish in size towards the outer 

 margin very much more markedly than in our species. On the whole 

 we cannot think that the evidence for the identity of these two 

 Vertigos is at present conclusive. 



( To be continued). 



1 Jahrb. Nassau. Verein Naturk. Jahrg. 42, p. 307. 



2 Bull. U.S. Nat. Museum, 28 (1885), p. 192. 



