PULMONATA. 75 



No. 25. Achatina costellata. Sowerby. Tab. XII, fig. 1 a — h. 



Bulimus costellatus. Sow. Min. Con., vol. iv, p. 89 bis, t. 336. 

 Limnea maxima. Sow. lb., vol. vi, p. 53, t. 528, fig. 1. 

 Bulimus costellatus. Morris. Cat. of Brit. Foss., p. 140. 

 Limn^us maximus. Morris. lb., p. 148. 



A. testa ovato-oblonyd, apice sub-acuto ; anfractibus sex convexiusculis, lonyitudinaliter 

 costellatis, ad suturam adpressis et irreyidariter sub-cremdatis ; costellis parum obliquis, 

 irreyularibus : aperturd pyriformi, dimidium totius testa in lonyitudinem fere aquanti, 

 maryine externo undato. 



Far. abbreviata. Fig. 1 i — k. A. testa ventricosiori, breviori ; anfractibus quinque, 

 convexioribus ; aperturd lonyiori, spiram in lonyitudinem superanti. 



Shell oval-oblong, with a somewhat acute apex ; the six volutions, of which the 

 spire is formed, are more or less convex in different individuals, and are longitudinally 

 ribbed ; the edges are slightly pressed against the preceding volution, so as to 

 present a narrow band running round the spire, parallel with the suture ; the ribs are 

 rounded, irregular, rather oblique, and slightly thickened above the sutural band, 

 giving a rough crenulated appearance to the edges of the volutions ; they are crossed, 

 saltierwise, by very faint obscure lines of growth, perceptible only in well-preserved 

 specimens. The aperture is pear-shaped, and about half as long as the entire shell ; 

 the outer lip undulated. The truncation of the columella, a character which the 

 imperfect state of the specimens figured by Mr. Sowerby did not enable him to detect, 

 places the shells, described by that author as Limnea maxima and Bulimus costellatus, 

 in the present genus. The volutions are variable, being in some specimens less convex 

 than in others ; and the aperture in the young state is comparatively longer than that 

 of the mature shell. A similar change in the relative proportions of the spire and the 

 aperture at different stages of growth is not of infrequent occurrence, and is exhibited 

 in some of the recent species in this genus, particularly in Achat, striata, (Glandina 

 truncata, Pfeiffer.) These considerations, confirmed by the examination of along series 

 of shells of the present species in different stages of growth, have induced me to 

 consider Bui. costellatus as merely the young form of the shell figured as Limnea 

 maxima. The more regularly conical form of the spire, the only distinction by which 

 the former is separable from the latter, is mainly due to the preservation of the shell 

 in the specimen figured, and is a character which cannot be relied upon. 



The present species belongs to the group constituting the genus Glandina, and is 

 another instance of the approximation of an European Eocene land Mollusc to the 

 living forms of the Western world. 



Size. — Axis 2j inches, nearly; diameter 9-lOths of an inch. 



The specimen represented by figs. 1 i and 1 k, resembles the type in the crenulated 



