PULMONATA. 79 



slightest pressure, as the animal emerges from the shell, and the clausium is then 

 bent back against, and fits upon, the curved columella, but recovers its former position 

 by the recoil of the pedicle on the removal of the pressure when the animal withdraws 

 itself into the shell. This peculiar appendage was described first by D'Aubenton, and 

 subsequently by Muller; and the group of shells characterised by its presence was 

 formed by Draparnaud into the present genus.* 



The animal of Clausilia, so far as its organisation is known, resembles that of Pupa, 

 but Lamarck considered that the differences in the form and condition of the aperture 

 to which I have already referred, were in themselves sufficient for generic distinction 

 without reference to the presence of the clausium. On the other hand, Ferussac has 

 placed Clausilia in his genus Helix, where it forms part of his sub-genus Cochlodina ; 

 and M. Deshayes has been induced, by the resemblance between the external characters 

 of the animals, by the similarity of their habits, and by the gradual passage from the 

 one genus to the other by intermediate species, to propose the union of the two genera. 

 Unless, however, peculiarity of structure or form in the shell is to be altogether 

 disregarded, the presence of so singular an appendage as the Clausium must surely be 

 considered as sufficient ground for the separation of this genus. 



Nearly two hundred living species, mostly small shells, are known ; several are 

 found in this country, but they occur in great profusion in Southern Europe ; the larger 

 species belong to tropical climates. 



Only three fossil species I believe have as yet been described ; viz., C. antiqua, from 

 the Freshwater limestone of Ulm ; C. maxima, from the neighbourhood of Dax, and 

 C. campanica, from the Freshwater limestone of Provins, in which the Paleotherian 

 remains occur. 



No. 28. Clausilia striatula. F. E. Edwards. Tab. XI, fig. 6 a — h. 



CI. testa subturritd, cylindracea, ad utramque extremitatem attenuatd, transversim 

 lineatd .• anfractibus numerosis, plano-convexis, ultimo ad basin porrecto ; aperturd ovato- 

 pyriformi, obliqud; peristomate soluto, parum reflexo : lamellis quinque, duobus margine 

 externo, tribus margine columellari, instructo. 



A cylindrical, subturreted shell, attenuated at each extremity ; the whorls are very 

 slightly convex, and covered with numerous rather oblique raised lines, separated by 

 broad rounded sulci, occasionally confluent ; the last whorl detaches itself, and projects 

 obliquely forward, terminating in an ovate, pyriform aperture, the margins of which 

 are free, and a little reflected. The outer lip presents two unequal plait-like teeth, 

 the smaller one near the middle, the larger one near the posterior angle of the 



* A particular account of the Clausium has been given by Mr. Miller, in the 'Annals of Philosophy,' 

 vol. iii, p. 378; and by Mr. J. E. Gray, in the 'Zoological Journal,' vol. i, p. 212. 



