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Show 1874.] NEW SPECIES OF HELICIDJE. 611 ridge, with slight notches both above and below. A long horizontal lamella is given off from centre of the apertural ridge and extends up to, but does not unite with the vertical parietal lamina ; this is simple, toothed on the vertical edge, curving above slightly backwards, and giving off a short horizontal lamella from the lower end towards the aperture ; a thread-like free lamina, rather longer, runs parallel to it below. Palatal teeth simple, 6 in number, the three lowest the longest and highest, the sixth much arched outwards. Major diam. 0'50 inch, minor diam. 0'43, alt. axis 0' 19. Hab. Discovered by Mr. W . T. Blanford at Thayatmyo, in Pegu, who has kindly allowed m e to describe it. This well-marked species is a close link to P. perarcta ; but the lowest free lamella does not extend up to the aperture to unite there with the parietal ridge as in that shell. The vertical parietal lamina is remarkably toothed in all the shells I have examined, and the principal long horizontal lamella is unbroken throughout. I have before alluded to an occasional reduplication of structure when describing Plectopylis serica, which reduplication seems to have played an important part in the development of the different species, such a change becoming at last permanently established. This is apparent on an examination of the species from north to south, those from Burmah showing a structure more complicated and with internal barriers more solid. The Himalayan, Khasi, and North-Burma forms are the simplest*, while in P. cyclaspis, kare-norum, achatina, and feddeni they have assumed the most complicated form. In P. feddeni the parietal barrier is evidently a combination of three parallel vertical laminae, the two anterior of which are first united above and below by horizontal lamellae, the enclosed area becoming eventually filled with shelly matter. At the same time, in these last species the tendency that is seen in many species to obliquity in the normal horizontal parallel palatal plicae has at last produced, as the representative of the fourth and fifth plicae, one solid and nearly vertical lamina, situated immediately in front of the interval between the vertical parietal lamina?. It seems difficult to account for the use of the extremely contracted internal form of the last whorl, as seen so largely and intricately developed in this group of the Helicidae. W h e n breaking up a number of shells to expose the barriers, and ascertain if their characters were constant, I was greatly interested to find in two instances the presence of small insects that had become fixed between the sets of teeth ; it has occurred to m e that this is a probable solution, and perhaps one of the uses which the barriers serve, and to this end have been developed. Insect life swarms in the forests where the shells are found ; and it is quite possible that certain kinds of beetles, ants, or even leeches, prey upon the mollusca, and that those possessing such bars to their predatory visits, supplemented by the mucous secretion which the * Tbe two small forms from South India and Ceylon assimilate to these, but differ in the arrangement of the palatal plica. |
