PLECTOPYLIS. 71 



and elongate, the heart situated one whole whorl behind the 

 aperture, and lying below the oval-shaped kidney. The oviduct 

 was packed close to the heart. 



The jaw he found very thin and delicate, composed of 24 

 elongate plates which slightly overlap, the central plates being the 

 largest. These plates were attached to a mass of muscular tissue , 

 or, in other words, this muscular tissue merged into the more 

 solid plates ; in this respect there being a similarity to the jaw 

 of Succinea ; the resemblance to the ja\v of Tliysanota guerini 

 being still greater. 



The teeth of the radula are stated to be thus disposed : 

 12. 9. 1.9. 12 or 21. 1.21. 



The centre tooth is stated to be small, on a narrow oblong 

 plate; the plates of the admedian teeth nearly square, there being 

 an indication of a duplication followed by fusing of parts, the 

 square plate being divided into a long inner oblong portion and a 

 shorter outer oblong portion with a well-defined rounded upper 

 outer angle. At the 10th tooth the very long inner cusp of the 

 9th tooth he found to become bicuspid into blunt rounded points, 

 the biscuspid form with a single small cusp outside it continuing 

 to the outermost teeth. This type of radula, he notes, is peculiar 

 to the genera Tliysanota^ Sylcesia [JRuthvenia], and Philalanka, to 

 a greater or less extent with modification of the central and 

 admedian teeth. 



Stoliczka raised Plectopylis to generic rank, but Prof. Pilsbry 

 in 1890 made it a section of Helix. In 1894, however, he also 

 accorded it generic status and in his Index to the Helicidae, 1895, 

 p. 124, it was placed between the groups Macroogona and Teleo- 

 phallogona. He there included two Chinese groups of uncertain 

 affinity Traumatopliora and Stegodera, each containing one 

 species but as nothing is known of their anatomy, and as, more- 

 over, they are devoid of the armature characteristic of Plectopylis, 

 their inclusion is hardly warranted. 



In 1899 the present writer divided the genus into seven sections, 

 one of which Sylcesia [Jtuthvenia~] has since been shown to have 

 affinity with Tliysanota and Pliilalanka and which has already been 

 dealt with (ante p. 25). Another section Enteroplax, proposed 

 for the reception of three Philippine Island species will probably 

 share a similar fate when the soft parts come to be examined. 



Benson had already noted that Plectopylis achatina [bensoni] 

 was ovoviviparous, and this was found to be the case with all four 

 species examined by Stoliczka. I have also observed this fact in 

 a specimen of P. lissochlamys. 



As regards the question concerning the probable primordial 

 form from which the existing species have been evolved, this 

 is very problematical, as no fossil forms are known. Stoliczka, 

 it is true, described three species of fossil Helices, which he 

 referred to the section Ancliistoma [= Gonostoma~\, stating 

 that they had affinity with Plectopylis and Gorilla (Cretaceous 



