7 o 



SCIENCE-GOSSIP. 



ARMATURE OF HELICOID LANDSHELLS, 



With New Species of Plectopylis. 



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



(Continued from page 37.) 



pLECTOPYLIS magna (>■) (figs. 52a-/). With 



a miscellaneous collection of Plectopylis, 



from Burma, kindly sent to me by Miss 



Fig. 52.— Plectopylis magna. 



Linter, Arragon Close, Twickenham, were two 

 forms which appear to be undescribed, and, 



(') Pkctopylis magna, n. sp. (figs. 52rt-/).— Shell sinistral, 

 solid, discoid, widely and deeply umbilicated, horny brown, 

 finely and regularly ribbed. Suture slightly impressed, spire 

 depressed, apex scarcely raised. Whorls yh, a little rounded 

 above, tumid below, increasing very slowly, "the last widening 

 a little towards the aperture, descending somewhat slowly in 

 front, and a little constricted behind the peristome. Aperture 

 elliptical, peristome white, thickened and reflexed, margins 

 scarcely converging. Parietal callus with a raised flexuous 

 ridge, separated from both margins of the peristome by a 

 little notch. Umbilicus wide and deep. Parietal wall with 

 a short, entering, flexuous, horizontal fold, which terminates 

 at a distance of two millimetres from the parietal ridge at 

 the aperture, and having at one-third of the circumference 

 from the aperture two strong transverse plates ; the 

 posterior one the longest, vertical, and a little flexuous, 

 giving off a short, obliquely raised ridee posteriorly above, 

 and a short, strong, obliquely deflexed ridge posteriorly below ; 

 the anterior one oblique, the upper extremity converging 

 towards the posterior plate, where it gives oft posteriorly a 

 short, strong ridge, and anteriorly a strong, longer ridge, 

 which becomes attenuated ; at the lower extremity it gives 

 off two short, strong ridges, one posteriorly and one anteriorly ; 

 below these plates occurs a thin fold, close to the lower 

 suture, revolving as far as the aperture, where it unites with 

 the flexuous ridge. Palatal folds, 5: the three upper 

 horizontal ; the first straight and having an elongated denticle 

 below it at about the middle; the second a little deflected 

 posteriorly ; the third short, crescent-shaped ; the fourth 

 vertical, flexuous; the fifth horizontal, abruptly deflexed 

 anteriorly above and posteriorly below. Posteriorly between 

 the first and fifth folds occur six denticles, placed vertically 

 in a row, the first in a line with the elongated denticle below 

 the first fold, the second a little above and the third a little 

 below the second fold, the fourth in a line with the upper 

 extremity, the fifth near the middle, and the sixth a little 

 below the lower extremity of the vertical fold. — Major 

 diameter, 22*5-25 millimetres; minor diameter, 18*5-21 milli- 

 metres ; axis, 8 millimetres.— Habitat, Burma.— Type in my 

 collection. 



although closely allied to each other and to 

 Plectopylis ponsonbyi {ante vol. iii., page 178), they 

 present sufficient differences to warrant their being 

 regarded as distinct. Three of the specimens in 

 question belong to the form which I now publish 

 as a new species under the name of Plectopylis 

 magna. A shell in the collection of Mr. E. R. 

 Sykes, which had been labelled P. achatina, I also 

 refer to this species. This new form differs from 

 P. ponsonbyi in being much larger, more solid, and 

 darker in colour, in having one whorl more, in the 

 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 plates are convergent above, and the 

 posterior one is considerably longer than the 

 anterior one (see fig. 52c), while in Plectopylis 

 ponsonbyi they are almost equal and parallel ; the 

 anterior plate gives off anteriorly below a short, 

 stout ridge, not a distinct fold as in P. ponsonbyi, 

 and the thin fold near the 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 

 short and crescent-shaped, and the vertical fold is 

 not bilobed, while there are several more denticles 

 posteriorly (see fig. 52/, which shows the inside of 

 the outer wall). The specimen figured, received 

 from Miss Linter, as above mentioned, is in my col- 

 lection, and measures 25 millimetres in diameter 

 A second specimen measures 225 millimetres in 

 diameter. The third specimen is not quite mature, 

 the ridge on the parietal callus at the aperture not 

 being formed, but the armature is quite identical 

 with that of the mature shells. Figs 52a, b, c and e 

 are natural size, figs. 52^ and/ are magnified. 

 Plectopylis lissochlamys (-j (figs. 53a-/). The form 



( 2 ) Plectopylis lissochlamys, n. sp. (figs. 53a-/). — Shell 

 sinistral, solid, discoid, widely and deeply umbilicated, 

 polished, corneous, finely and regularly ribbad, decussated 

 with minute spiral sculpture aDove. Suture impressed, 

 apex a little raised, spire depressed. Whorls 7, rounded, 

 increasing slowly, the last twice as wide as the penultimate, 

 widening towards the aperture, but not constricted behind 

 the peristome. Aperture rounded, elliptical ; peristome 

 white, rather thin, reflexed ; margins a little converging. 

 Parietal callus with a raised flexuous ridge separated from 

 both margins of the peristome by a little notch. Umbilicus 

 wide and deep. Parietal wall with a short, entering, flexuous 

 horizontal fold, which runs close up to the ridge at the 

 aperture, and at one third of the circumference from the 

 mouth there are two rather thin transverse parallel plates, 

 descendingobliquely backwards, the posterior one longestand 

 with a short ridge posteriorly both at the upper and the lower 

 extremities; the anterior one with a longer ridge anteriorly 

 at the upper extremity, and two short but stouter ridges at 

 the lower extremity, one anteriorly and one posteriorly 

 below these plates occurs a thin horizontal fold close to the 

 lower suture, becoming attenuated but distinctly perceptible 

 at the aperture, where it unites with the flexuous ridge. 



