— 
t 
PULMONATA. 
No. 25. ACHATINA COSTELLATA. Sowerby. Tab. XII, fig. 1 a—/. 
BuLIMUs cosTELLATUS. Sow. Min. Con., vol. iv, p. 89 bis, t. 336. 
Limnea Maxima. Sow. Ib., vol. vi, p. 53, t. 528, fig. 1. 
Butts costevLatus. Morris. Cat. of Brit. Foss., p. 140. 
Limn2us Maximus. Morris. Ib., p. 148. 
A. testa ovato-oblongd, apice sub-acuto ; anfractibus sex convexiusculis, longitudinaliter 
costellatis, ad suturam adpressis et irregulariter sub-crenulatis ; costellis parum obliquas, 
irregularibus: aperturd pyriformi, dimidium totius teste in longitudinem Jeré equant, 
margine externo undato. 
Var. ABBREVIATA. Fig. 1i—kh. A. testa ventricosiori, breviort ; anfractibus quinque, 
convexioribus ; apertura longiort, spiram in longitudinem superantt. 
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 Zimnea 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 Lu. 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 G/andina, and is 
another instance of the approximation of an European Eocene land Mollusc to the 
living forms of the Western world. 
Size.—Axis 2} inches, nearly ; diameter 9-10ths of an inch. 
The specimen represented by figs. 17 and 14, resembles the type in the crenulated 
