170 



SCIENCE-GOSSIP. 



ARMATURE OF HELICOID LANDSHELLS 



AND NEW FORMS OF PLECTOPYLIS. 

 By G. K. Gude, F.Z.S. 



{Coiiliinied from page 135.) 



pLECTOPYLIS Unterae (figs. 8Srt-f), from Pegu, 

 was described by Dr. von Mollendorff in the 

 " Nachrichtsblatt der Deutschen Malakozoologi- 

 schen Gesellschaft," 1S97, p. 28. The shell is 

 sinistral, solid, discoid, widely umbilicated, pale 

 yellow, transversely streaked and flammulated 

 with chestnut, finely and regularly ribbed, smoother 

 below, decussated with microscopic spiral lines. 

 The spire is slightly conical, the apex scarcely 

 produced, and the suture linear. There are six 

 whorls which increase slowly and regularly, and 

 are a little flattened above and rounded below ; 

 the last is slightly angulated above the periphery 



Fig. SS.—PkciopyUx liii/erae. 



and around the umbilicus, and descends rather 

 abruptly and deeply in front. The aperture is 

 oblique, heart-shaped. The peristome is white, 

 thickened and strongly reflexed ; its margins are 

 united by a strong flexuous raised ridge on the 

 parietal callus. The parietal armature is composed 

 of a slight median horizontal fold, which proceeds 

 from the apertural ridge, is interrupted for a short 

 distance and then continues parallel with the 

 suture for about a quarter of the last whorl ; it then 

 gives off a shortly descending, slightly reflexed 

 arm, which is provided anteriorly at the lower 

 extremity with a short horizontal ridge; the fold 

 then rises obliquely for a short distance and finally 

 bifurcates ; the lower arm of the hifiircation is the 

 longer, and descends obliquely, its lower extremity 

 being provided posteriorly with a short horizontal 

 ridge ; the upper arm at first continues to ascend 

 obliquely, then deflects horizontally close to the 

 suture ; a short, free, thin, horizontal fold occurs 

 below the two lower arms, not extending beyond 

 on either side (see fig. 8gd, which .shows the parietal 

 wall with its folds). The palatal armature consists 

 of : first, a thin long horizontal fold near the 

 suture and parallel with it ; secondly, a shorter 

 but stronger broad horizontal fold, which deflects 

 a Utile and is slightly indented posteriorly ; 

 thirdly a still shorter, broad, straight horizontal 

 fold ; fourtb.lj, a strong broad vertical plate, 

 which intercalates between the two lower arms of 



November, 1898.— No. 54, Vol. V. ' 



the parietal fold ; this plate is inclined towards 

 the aperture, and its edge is thickened and reflexed ; 

 near its lower extremity on the posterior side 

 occurs a strong little denticle, which is elongated 

 horizontally ; fifthly, a short thin horizontal fold 

 close to the lower suture, having an elongated den- 

 ticle a little above its posterior extremity. The 

 species is closely allied to Plectopylis achat ina, but 

 the spire of the present shell is much more raised, 

 the umbilicus is much deeper, and the whorls more 

 rounded. In the armature this species further 

 differs from P. achatina in the median parietal fold 

 being interrupted and much slighter, the branched 

 portion being relatively much more elevated ; the 

 lower free horizontal parietal fold is very short, so 

 that this part of the armature, while differing 

 from the typical forms of P. achatina, recalls the 

 condition which obtains in the var. brevipUca of 

 that species. The specimen figured, which I 

 received from Miss Linter, was labelled with 

 the habitat, " Moulmain." It measures : major 

 diameter, 16 millimetres ; minor diameter, 13 

 millimetres ; altitude, 6 millimetres. 



Plectopylis linteiae var. fusca (i) (figs. Sga-f). Mr. 

 Ponsonby possesses a shell labelled P. paehystoma 

 var. minor, which I am unable to separate speci- 

 fically from P. Unterae, but which differs from 



d e / 



Fig. 89. — Plccti'pylis Unterae, var. fusca. 



the typical form of that species in being of a 

 unicolorous dark-brown, in the peristome being 

 livid instead of white, and in the shell being 

 thinner in texture. The armatures are identical 

 in both forms. Fig. Sgd shows the parietal wall 

 with its folds, while fig. 89^ gives the anterior, and 



(1) Plectopylis lintcrat: var. fusca, n. var. (figs. 8917-/), differs 

 from the type in being unicolorous dark-brown, a little paler 

 below, in being thinner in texture, and in tlie peristome 

 being livid. Major diameter, i4'5 millimetres ; minor 

 diameter, 12-5 millimetres ; altitude, 5'5 millimetres. — 

 Habitat, Burma. =Type in Mr. Ponsonby's collection 



