SCIENCE-GOSSIP 



15 



ARMATURE OF HELICOID LAXDSHELLS 



AND NKW SPECIKS OF PLECTOI'VLIS. 

 By G. K. (;ii>E, F.Z.S. 



(Continui-d fioiti I'ol. I'., /xtcf JJJ.J 



PlectopyHx aiislcni (') (figs, gja-f.j. F'our speci- 

 mens, three adult, one yoiuii^, of an unnamed form of 

 Plectopylis, difterini^ from all described species, have 

 been kindly placed in m\' Inands 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 PUclopylis oglci (figured in 

 SciENCE-Gossii', N.y. iv. (1898) p. 263, fig. 68), but 

 it can readily Ije 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 aiisfeiii has further some affinity, as re- 

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



O} 



Fig-. 97. — Plectopylis aiistfiii. 



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

 but the latter is a dextral species and the parietal 

 armature is tjuite different, as also in the general shape 

 nf the shell. The immature specimen of /'. aiisteni 

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

 w lie iris, 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 onh' of the vertical 

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

 of it. The palatal armature is similar to that of 



(1) Plectopylis aiistciii, n.sp. (figs, qja-f). — Shell 

 sinistral, discoid, widely umljilicated, ochreous cor- 

 neous, covered with a deciduous velvety cuticle ; 

 finelv and closely ril)bed, 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 

 Jin:-;. 1859. — No. ()i. \'oI. \'l. 



mature shells, except tiuu the folds, ridge and 

 denticles are very small and slight. Lieut. -Col. 

 Godwin- Austen informs me that the shells were 

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

 \ alley, Singpho, Assam. 



Plectopylis ivoodthorpei (-) (figs. 98 a-Ji). Three 

 specimens — two mature, one young — another unde- 

 scribed form of Plectopylis, have also Ijeen most 

 obligingly sent to me for examination by Lieut. - 

 Colonel Godwin-Austen, who informed me that they 

 were collected in 1894 b_\- 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 poiisonbyi and that of /'. plectostoiiia ; on the one 

 hand it resembles /'. poiisonbyi in the posterior 

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

 /'. leiicochihi in iis parietal armature (see fig. 98 t') ; 

 it differs, however, from the other members of this 

 group in having a series of horizontal folds anteriorh 

 to the vertical palatal plate. On the other hand, 

 this biseriatecharacter of the last-mentioned structure, 

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

 ward appearance the shell of /'. woodthoipei nuich 



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

 apex a little raised, suture strongl)' impressed. Whorls 

 6^, flattened above, roiinded below, obsoletel}- angu- 

 laled around the umbilicus ; increasing slow I_\- at first, 

 the last widening rather suddenly, and descending half 

 the width of the whorl in front ; aperture oblique, 

 cordate. Terislome white, strongly thickened and 

 reflexed, the margins united b)- a strong laised flcxuou.s 

 concave ridge, slightl)' 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 low er extremiiies of which 

 are deflected posteriorly. Palatal armature composed 

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

 suture, provided at its posterior extremit)- with an 

 elongated denticle ; the second, third, fourth, and 

 fifth a little oljliquely depressed posteriorly where the_\- 

 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, 

 w hile the fifth is situate near the upper extremity of 

 the \ertical 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. — Plabitat, Diyung \'alley, .Singpho, Assam. — 

 Type in the Natural Histoiy Museum, Sou.th Ken- 

 sington. 



