SCIENCE-GOSSIP. 



IS 



ARMATURE OF HELICOID LANDSHRLLS 



AND NEW SrECIES OF I'LECTOl'MJS. 

 By G. K. GuDE, K.Z.S. 



(Continued from ]'ot. I'., fiu.^f SS3-J 



rUilopytis austeiii (') (figs. Cf^a-f.). Four speci- 

 mens, three adult, one. young, of an unnamed form of 

 ricctopylis, differing from all described species, have 

 been kindly placed in my liands for examination by 

 Lieut. -Col. Godwin-Austen, with whose name I have 

 much pleasure in associating this new species. The 

 new shell is allied to PUc/opylis oglei (figured in 

 SciENCE-Gossif, N.S. iv. (iSgSjp. 263, fig. 68), but 

 it can readily be distinguished from that species by its 

 concave spire ; it is also much smaller and much 

 more flattened. In its parietal armature, it differs in 

 having a short and a long median horizontal 

 fold and a denticle in front of the vertical 

 plate, all of which structures are absent in Plectopylis 

 oglei. A comparison of the figures will also indicate 

 differences in the palatal armatures of the two species. 

 Plectopylis austeiii has further some affinity, as re- 

 gards palatal armature, with /'. niuspratti (c.f. 



<cZ=Il 



Fio- 97- — Plectopylis austeni. 



SciEN'CE-Gossir, N.S. iv., 1897, p. 10, f. 45), 

 but the latter is a dextral species and the parietal 

 armature is quite different, as also in the general shape 

 of the shell. The immature specinien of P. austeiii 

 referred to above has completed five-and-a-half 

 whorls, and is interesting from possessing two sets of 

 armature a quarter of a whorl distant from each other ; 

 these differ considerably from the mature barriers ; 

 the parietal armature here consists only of the vertical 

 plate and a very short, slight, horizontal fold in front 

 of it. The palatal armature is similar to that of 



(') Plectopylis austeiii, n.sp. (figs, gya-f). — Shell 

 sinistral, discoid, widely umbilicated, ochreous cor- 

 neous, covered with a deciduous velvety cuticle ; 

 finely and closely ribbed, decussated by raised spiral 

 lines, rather distant on the upper side. One of these 

 spiral lines forms a ridge or keel on the upper angle 

 of the whorls above the periphery, revolving above 



mature shells, except that the folds, ridge and 

 denticles are verj' small and slight. Lieut. -Col. 

 Godwin-Austen informs me that the shells were 

 collected by his assistant, Mr. M. T. Ogle, in the Diyung 

 Valley, Singpho, Assam. 



Plectopylis woodthorpei (-) (figs. gS a-h). Three 

 specimens — two mature, one young — another unde- 

 scribed form of Plectopylis, have also been most 

 obligingly sent to me for examination by Lieut. - 

 Colonel Godwin-Austen, who informed me that they 

 were collected in 1894 by the late Colonel Wood- 

 thorpe, R.E. , after whom they are now named. This 

 new species is a very interesting one forming as it 

 does a connecting link between the group of Plecto- 

 pylis poiisoiihyi and that of P. plectostoiiia ; on the one 

 hand it resembles /'. ponsoiibyi in the posterior 

 portion of the palatal armature (see fig. 98/), and 

 P. leucochila in its parietal armature (see fig. 98 e) ; 

 it differs, however, from the other members of this 

 group in having a series of horizontal folds anteriorly 

 to the vertical palatal plate. On the other hand, 

 this biseriate^character of the last-mentioned structure, 

 unites it it with the group of /'. plectostoiiia. In out- 

 ward appearance the shell of P. woodthorpei much 



the suture as far as the third whorl. Spire concave, 

 apex a little raised, suture strongly impressed. Whorls 

 6A, flattened above, rounded below, obsoletely angu- 

 lated around the umbilicus ; increasing slowly at first, 

 the last widening rather suddenly, and descending half 

 the width of the whorl in front ; aperture oblique, 

 cordate. Peristome white, strongly thickened and 

 reflexed, the margins united by a strong laised floxuous 

 concave ridge, slightly notched at the junctions above 

 and below. Umbilicus wide and rather shallow. 

 Parietal armature consisting of a short median hori- 

 zontal fold close to the apertural ridge, and a second 

 longer one farther back, rather elevated posteriorly, 

 gradually descending on the shell wall anteriorly ; 

 below its posterior extremity occurs a small denticle ; 

 still farther back is found a strong vertical crescent- 

 shaped plate, the upper and lower extremities of which 

 are deflected posteriorly. Palatal armature composed 

 of six short horizontal folds, the first longest, near the 

 suture, provided at its posterior extremity with an 

 elongated denticle ; the second, third, fourth, and 

 fifth a little obliquely depressed posteriorly where they 

 are united by a slight vertical ridge, which is con- 

 tinued above the second and below the fifth folds ; 

 on the posterior side occur five elongated denticles, 

 the four lower of which correspond to the four folds, 

 while the fifth is situate near the upper extremity of 

 the vertical ridge ; the sixth fold is near the lower 

 suture, and has also an elongated denticle posteriorly. 

 — Major diameter, I7"5-I9 millimetres; minor dia- 

 meter, i475-i6'5 millimetres; altitude, 5-6 milli- 

 metres. — Habitat, Diyung Valley, Singpho, Assam. — 

 Type in the Natural History Museum, South Ken- 

 sington. 



