i6 



SCIENCE-GOSSIP. 



resembles P. shiroieusis {c.f. Science-Gossip, N.S. 

 iii., 1896, p. 155, f. 20), but the former is much 

 larger. The immature specimen referred to, wliicli 

 has nearly six whorls formed, has the armature in- 

 complete, and is instructive as possibly throwing 

 some light upon the evolution of these structuies. 

 The parietal armature here possesses the two vertical 

 plates, but the horizontal folds given oft by the 

 anterior plate are very short, being only one (juaiter 

 of the length of those in the mature shells ; the thin 

 fold near the lower suture is not compressed into a 

 lamellar fold below the vertical plates, as is the case 

 in the full-grown shells, and it rises much farther 

 back (see fig. 98 g., which shows portion of the 

 parietal wall with its armature . Of the palatal 

 armature, only the posterior series ot pro- 



~^ 



0^ 



Fig-. 98. — Plcctopyiis 7voodthorpei. 



cesses is present, the anterior series having 

 still to be formed : a fact clearly pointing 

 to the more recent origin of the biseriate forms. 

 The vertical plate is distinctly divided into two sub- 

 equal portions, in consequence of the indentation in 

 the middle being carried down to the base ; the ridge 

 connecting the upper extremity of the vertical plate 

 with the short horizontal fold above it is absent, but 

 in its stead occurs near the latter a little denticle ; 

 while posteriorly to the upper half of the vertical 

 plate is found a distinct denticle, corresponding to 

 the slight swelling in the same place, mentioned in 

 the diagnosis {see fig. 98/2, which shows the inside 

 of the palatal wall with its armature). 



Plectopylis {Sykesia) biciliala (figs. 99 a-e) from 

 Ceylon was described by Dr. Pfeifter in the " Pro- 

 ceedings of the Zoological Society,"' 1855, p. 112, as 

 Heli.y biciliatii, and the shell is figured in " Ilanley 

 and Theobald's Conchologia Indica '' (1875), t. 159, 

 figs. I and 4. The systematic position of this shell 

 remained uncertain for a long time ; it was placed in 

 iV(7///;/« by Dr. Pfeifter (" Malak. Blatter" ii., 1855, 

 p. 121), and in Discus., by Mr. H. Nevill (" Enum. 

 Helic. Ceylan."" 1871, p. i), while finally Mr. S. 

 Clesiin grouped it v\ith Macrochlainys (" Nomencl. 

 Helic. viv." 1881, p. 45). It is unfortunate that 

 Dr. Pfeiffer's types of this species cannot be found. 

 They were described as from the late Major Skinner's 

 collection, but Miss Linter who purchased the entire 

 collection, kindly informs me that the shells in 

 (juestion are not in it, and she does not think that 

 Major Skinner ever possessed them there being no 

 record of them in his catalogues. Mr. Edgar Smith 



(-) Pleclopylis zvoodthorpei, n. sp. (figs. 98 a-h). — 

 Shell dextral, discoid, widely and deeply umbilicated, 

 dark corneous, finely and regularly ribbed, closely 

 decussated by microscopic spiral lines. Spire conical, 

 apex prominent, suture impressed. Whorls 6A, in- 

 creasing slowly and regularl}', flattened above, tumid 

 bel<nv, the last scarcely wider than the penultimate, 

 bluntly keeled above the periphery, widening a little 

 towards the aperture, descending deeply in front. 

 Aperture oblique, cordate ; peristome whitish, 

 strongly thickened and reflexed, the margins united 

 bv a strongly raised flexuous ridge, which is concave 

 in the middle, and notched at the junctions above and 

 l)elow. Parietal armature consisting of two nearly 

 parallel vertical plates, the posterior one longer, 

 slightly reflexed posteriorly at its lower extremity, 

 and provided posteriorly at the upper extremity with 

 a slight ridge ; the anterior one shorter, giving oft a 

 horizontal fold anteriorly at each extremity, the 

 lower less than half the length of the upper, ascend- 

 ing obliquely : the upper revolving almost parallel with 

 the suture, toUowing the deflexion of the whorl, and 

 joining the ridge at the aperture. Below the posterior 

 vertical plate rises a free, thin, horizontal fold, at 

 first considerably elevated above the shell-wall, but 

 suddenly becoming attenuated and threadlike, run- 

 ning parallel with the lower suture, as far as the 

 aperture where it is joined to the ridge on the parietal 

 callus. Palatal armature in two series, the posterior 

 series consisting of : first, a long thin horizontal 

 iold near the suture ; secondly, a very long hori- 

 zontal fold, extending anteriorly beyond the 

 folds of the second series, with an elevated 

 compressed denticle posteriorly ; thirdly, a very 

 shor horizontal fold, deflexed posteriorly ; 

 fourthly, a strong vertical plate, with an in- 

 dentation at the middle, giving oft" posteriorly at its 

 lower extremity an obliquely descending ridge, and 

 provided at the same place with a small dentrcle ; at 

 the base of the upper lobe of the vertical plate ox\ the 

 posterior side occurs a slight swelling, while on the 

 same side from its upper extremity runs a short ridge, 

 connecting this plate with the thrrd horizontal fold ; 

 fifthly, a long thin horizontal fold near the lower 

 suture. The anterior series consists of three thin 

 horizontal folds, the first longest the third shortest, 

 all three descending a little anteriorly. — Major dia- 

 meter, S75-10 millimetres, minor diameter, 7^25-8 

 millimetres, altitude 3"25-4 millimetres. — Habitat, 

 Fort Stedman. Burma. — Type in the British Museum. 



