SCIENCE-GOSSIP. 



239 



ARMATURE OF HELICOID LANDSHELLS 



AND A NEW SPECIES OF PLECTOPYLIS. 



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



[Continued from page 172.) 



'"pHREE specimens of an unnamed Plectopylis 

 were submitted to me by Messrs. Sowerby 

 and Fulton, who state that they have unfortu- 

 nately no record of the origin of the shells. Upon 

 examination I found them to belong to an un- 

 described form, and I have now pleasure in 

 associating with this new species the name of Mr. 

 G. B. Sowerby [}). The present shell is closely allied 

 to Plectopylis plectostoma and P. affinis, a fact which 



d e f 



Fig- 93- — Plectopylis sowerbyi. 



led me to re-examine my own specimens of these 

 two species, and among a lot of P. plectostoma 

 received from Miss Linter in 1891, labelled 

 " Khasia Hills," I found a decorticated specimen 

 which undoubtedly belongs to the new species. 



(!) Plectopylis sowerbyi, n. sp. (fig. 93a-/.). — Shell 

 sinistral, widely umbilicated , discoid, dark corneous, 

 regularly ribbed and radiately distantly plaited, 

 strongly decussated above by spiral ribs, less 

 distinctly so below. Whorls six, narrow, increas- 

 ing slowly and regularly, somewhat flattened 

 above and rounded below, the last not descend- 

 ing in front. Six or seven spiral ridges, probably, 

 when fresh, bearing rows of hairs, pass round 

 the whole of the body-whorl, the first just above 

 the slightly angular periphery, the others below 

 it. Aperture ear-shaped ; peristome slightly 

 tinted with rosy-pink, scarcely thickened, and a 

 little reflexed ; the upper outer margin a little 

 depressed ; parietal callus slight, without raised 

 ridge at the aperture. Umbilicus deep and 

 wide. The parietal armature consists of a 

 strong vertical plate, provided at its lower ex- 

 tremity with a short support anteriorly, and a 

 small denticle posteriorly. The palatal arma- 

 ture is composed of six more or less horizontal 

 folds, the first very slight and short, near the 

 suture, the four next longer and more elevated, a 

 little deflexed posteriorly, the sixth slight and very 

 short. — Major diameter, 7-9 millimetres; minor 

 diameter, 6-25~7'5 millimetres; altitude, 3"75-4'75 

 millimetres. — Habitat, Khasia Hills, Assam. — Type 

 in my collection. 



P. sowerbyi can at once be distinguished from 

 P. plectostoma by the following characters : it is 

 flatter, being less raised in the spire ; the umbilicus 

 is more open ; there are only six whorls, the last 

 not descending in front ; the peristome is scarcely 

 thickened and not much reflexed, and there is no 

 raised ridge on the parietal callus. In the arma- 

 ture there are also important differences : the 

 vertical parietal plate in P . plectostoma gives off from 

 its upper extremity anteriorly a horizontal fold, 

 which is absent in P. sowerbyi, where the plate in 

 question is only provided with a support anteriorly 

 and a denticle posteriorly below, and there is no 

 horizontal fold below it ; so that in this respect 

 the present species differs from both its allies (see 

 fig. 93/, which shows part of the parietal wall with 

 its armature). The palatal armature is in one 

 series, and consists of six horizontal folds. The 

 first fold is very short and slight ; the second 

 longest ; the third, fourth, and fifth each a little 

 shorter than its predecessor ; the sixth slight and very 

 short (see fig. 93^, which shows the inside of the outer 

 wall with its folds). All the figures are enlarged. 



In addition to the specimen from the Khasia 

 Hills, mentioned above, I possess an immature 

 shell of unknown origin, which I also refer to 

 P. sowerbyi. The last whorl of this specimen is 

 nearly complete, but the armature, which is 

 identical with that of the mature shells, is situate 

 at half a whorl from the aperture. 



Plectopylis alphonsi (fig. 94), from the Province 



Fig. 94. — Plectopylis alphonsi. 



of Monpin, Eastern Thibet, was described by 

 Mr. G. P. Deshayes in the " Nouvelles Archives 

 du Museum d'Historie Naturelle de Paris," vi. 

 (1870), p. 22, and figured in the same work, ix. 

 (1873), t. 2, figs. 22-24. The species has not 

 hitherto been referred to the genus Plectopylis, but 

 the palatal armature clearly indicates its generic 

 position. Mr. Pilsbry (" Manual of Conchology," 

 ix. p. 211) has placed the species in the genus 

 Enlota, but this is doubtless owing to the fact that 

 Mr. Deshayes makes no mention of armature in 

 his diagnosis. Some time ago Mr. Gredler sent 



