SCIENCE-GOSSIP. 



7S 



ARMATURE OF HELICOID LANDSHELLS 



AND NEW SPECIES OF PLECTOPVLIS. 



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



(Continued froju page hy.) 



Pkdopylis {Sykesia) caliginosa (figs. \Ooa-e) from 

 Ambagamuwa, Ceylon, was described and figured b_\- 

 Mr. Sykes, in the ' ' Proceedings of the Malacological 

 Society of London," iii. (1898), p. 72, t. 5, ff. 21, 22. 

 The shell is lenticular, narrowly umbilicated, ochreous 

 corneous, opaque, very finely and regularly ribbed, 

 the ribs being rather more prominent above than 

 below ; it is acutely keeled at the periphery, with a 

 raised spiral line above the keel, quite close to it, as 

 far as the apical whorl. The spire is conical, the apex 

 obtuse, the suture impressed. There are five very 

 slowly increasing whorls, flattened above, tumid 

 below, the last scarcely wider than the penultimate, 

 not descending in front. The aperture is almost 

 vertical, lunate, and the peristome simple, acute. The 

 parietal armature consists of two simple, sub-vertical 

 plates which are somewhat thickened and truncate at 

 the lower, and attenuated at the upper extremities ; 

 these plates are separated by a distance of a quarter 

 of a whorl, and the posterior one is the stronger (see 



a b c 



d 



07 



Fig-. 100.— Pleetopylis caliginosa. 



fig. ioO(f, which shows the parietal wall with its two 

 plates). The palatal armature is in two vertica 

 series : the anterior series consists of an obliquely as- 

 cending short quadrate tooth near the peripherj-, and 

 below this an obliquely descending lamelliform tooth, 

 with a slight, horizontally elongated denticle below 

 its posterior extremity ; the posterior series is similar 

 to the anterior one, but the teeth are stronger and 

 thicker in the former, while there is in addition a 

 horizontally elongated denticle on the anterior side of 

 the upper tooth. The specimen shown in figs. 

 looa-c measures 6 millimetres in diameter, alt. 3 

 millimetres, and is in the collection of Mr. Ponsonby. 

 The armatures are figured from the type specimen in 

 the collection of Mr. Sykes, who kindly permitted me 

 to open the shell for the examination of the armature. 

 Pleetopylis [Sykesia] clathraittla, \-ar. compressa, 

 (figs, \o\a-c) was described and figured by Mr. 

 Sykes in the "Proceedings of the Malacological 



t., 5, ff. 13, 14- It 



Society," iii. (189S), p. 72, 

 Ai'G. 1899. — No. 6;, Vol. \'I. 



differs from the tvpe in being more elevated, in the 

 more convex spire and the narrower umbilicus, while 

 the raised ribs are scarcely visible. The armature is 



Figf. lor. — Pleetopylis clathratula var compressa. 



similar to that of the type. The specimen figured is 

 in ]Nh". Ponsonby's collection ; it measures 5 milli- 

 metres in diameter, altitude 2 '5 millimetres. 



Pleetopylis franqoisi (figs. i02(7-t') from Dco-ma- 

 Phuc, Tonkin, was described and figured by Dr. II. 

 Fischer, in the "Journal de Conchyliologie, xlvi. 

 (1898), pp. 214-218, ff. I, 3, 4 (part published March, 

 1899). The shell is dextral, deeply and widely um- 

 bilicated, corneous, striated, and decussated with 

 microscopic spiral lines above, which become obsolete 

 at the periphery, the lower surface smooth and a 

 little shining. The spire is depressed, conical, the 

 apex prominent and the suture distinctly impressed. 

 There are 7^ whorls, which increase slowly and regu- 

 larly, and are somewhat flattened above and tumid 

 below. The last whorl is at first obsoletely keeled 

 above the periphery and angulated at the umbilical 

 region near the parietal callus ; it descends shorth- 

 and suddenly in front. The aperture is a little 

 oblique, subcircular ; the peristome white, a little 

 thickened and reflexed, its margins united l>y a 

 parietal callus. The parietal armature is composed of 

 two strong, obliquely divergent, transverse plates, the 

 anterior one shorter, rounded at the upper and giving 

 off an anterior ridge at the lower extremity ; a short 

 thin horizontal fold occurs immediately above it ; the 

 posterior plate longer, truncate at the upper, attenuated 

 at the lower extremity. A free thin horizontal fold 

 occurs below these plates, terminating on the one side 

 just below the anterior plate, and on the other just 

 in front of the posterior plate. (See fig. \02d, which 

 shows part of the parietal wall with its armature). 

 The palatal armature consists of six folds ; the first, 

 rather short, thin, horizontal, near the suture ; the 

 second longest of all, horizontal, deflected at the 

 posterior extremity and becoming slowly attenuated 

 anteriorly ; the third, fourth, and fifth stronger, semi- 

 circular, oblique, their anterior extremities a little 

 reflexed, their posterior ones a little deflexed ; the 

 sixth thin, long, horizontal ; the second, third, fourth, 

 and fifth give oft", about the middle, from the lower 

 side, a slight callous ridge which connects them inter 

 se ; between the posterior eiitremities of the fi!th and 



D 4 



