78 On Proserpina opalina and Helix Proserpinula. 



takes place before the thickening of the lip, is shown in the 

 young shell of H. maxima. 



. What object the animals gain by this operation, I am at a 

 loss to conjecture, unless it be that they require more space for 

 the development of some organs at a certain stage of growth, 

 than the continued existence of the spiral column and septa 

 would permit. But I would ask whether any, and if so, what 

 structural peculiarity exists in the Terrestrial and other Mol- 

 lusks, in whose shells the spiral column and septa are removed, 

 which renders it necessary for them to effect such an alteration 

 of their habitations ? 



XIV. On PROSERPINA OPALINA C. B. Ad., and HELIX PRO- 

 SERPINULA Pfr. 



By T. BLAND. Read March 6, 1854. 



Having noticed (as explained in a paper lately read before 

 this Society) the removal of the spiral column and septa in 

 shells of six species of Proserpina (Pfeiffer enumerates eight 

 species in the third volume of his Monographia), I examined 

 the shells of P. opalina C. B. Ad., and Helix Proserpinula Pfr. 



The former shell was originally called Helix hyalina by 

 Adams (fide Pfeiffer in Monog.), in some schedule, of the date 

 of which I am ignorant, but was first described by Adams in 

 January, 1845, in the Proceedings of the Boston Society of 

 Natural History, as Helix opalina. In June of the same year, 

 Pfeiffer described it in the Zeitschrift as H. margarita. It was 

 included by Adams in his Catalogue of Jamaica Helicidse, pub- 

 lished in the Annals of the Lyceum, vol. v., and in the Contri- 



