]24 HELICID.E. 



last whorl descending less abruptly, and in the whorls being more 

 rounded. There are also differences in the armature, i. e. the two 

 parietal vertical laminae are convergent above, and the posterior 

 one is considerably longer than the anterior one (see tig. 60 e), 

 while in Plectopylis ponsonhi'i they are almost equal and parallel ; 

 the anterior lamina gives off anteriorly below a short, stout ridge, 

 not a distinct fold as in P. ponsonhyi, and the thin fold near the 

 lower suture is distinctly continued to the ridge at the aperture, 

 without becoming attenuated ; the two upper palatal horizontal 

 folds are much thinner, the third is very short and crescent-shaped, 

 and the vertical fold is not bilobed, while there are several more 

 denticles posteriorly (see fig. 60/, which shows the inside of the 

 outer wall). The type specimen figured is in my collection and 

 measures 25 mm. in diameter, a second specimen measuring 

 22-5 mm. A third specimen, from the same source, is not quite 

 mature, the ridge on the parietal callus at the aperture not having 

 been formed, but tlie armature is identical with that of the mature 

 shells. Figs. 60 a, 6, c, and e are of natural size, while d and / 

 are magnified. 



108. Plectopylis woodthorpei, Gude. 



Plectopylis woodtJiorpei, Gude, Science Gossip, x. s. vi, 1899, p. 15, 



fig. 98 (shell and armatm-e). 

 Plectopylis (s. s.) woodthorpei, Gude, torn. cit. p. 148. 



Original description : — " Shell dextral, discoid, widely and deeply 

 umbilicated, dark corneous, finely and regularly ribbed, closely 

 decussated by microscopic spiral lines. Spire conical, apex pro- 

 minent, suture impressed. Whorls 6^, increasing slowly and 

 regularly, flattened above, tumid below, the last scarcely wider 

 than the penultimate, bluntly keeled above the periphery, widening 

 a little towards the aperture, descending deeply in front. 

 Aperture oblique, cordate ; peristome whitish, strongly thickened 

 and reflexed, the margins united by a strongly raised flexuous 

 ridge, which is coucave in the middle, and notched at the junctions 

 above and below. 



" Parietal armature consisting of two nearly parallel vertical 

 laminae, the posterior one longer, slightly reflected posteriorly at its 

 lower extremity, and provided posteriorly at the upper extremity 

 with a slight ridge ; the anterior lamina shorter, giving off a hori- 

 zontal fold anteriorly at each extremity, the lower less than half 

 the length of the upper, ascending obliquely ; the upper revolving 

 almost parallel with the suture, following the deflection of the 

 whorl, and joining the ridge at the aperture. Below the posterior 

 vertical lamina rises a free, thin, horizontal fold, at first consider- 

 ably elevated above the shell-wall, but suddenly becoming attenu- 

 ated and thread-like, running parallel with the lower suture, as 

 far as the aperture where it is joined to the ridge on the parietal 

 callus. Palatal armature in two series, the posterior series con- 

 sisting of: first, a long thin horizontal fold near the suture; 



