21 



CHARACTEES OF TWO UNDESCKIBED LAND SHELLS FEOM 

 THE REPUBLIC OF COLOMBIA AND A NEW GENUS OF 

 HELICOIDS. 



By a K. Gdde, F.Z.S. 



Eead 12th January, 1912. 



The shells forming the subject of the present communication were 

 collected in the United States of Colombia at an altitude of 5,600 feet 

 near Alejandria, a place 50 miles from Medellin, by Mr. T. P. 

 Sharraan, a mining engineer, who is also a good naturalist and 

 sportsman. They were forwarded by him to Major A. J. Peile, who 

 sent them to me for identification, and as they appeared to be new to 

 science he obligingly placed them at my disposal for description. 



The first species belongs to a small group of Helicidae, of which 

 hitherto only three species were known, two of which Professor 

 Pilsbry assigned to Isomeria, namely, Pleurodo7ita vexans, Dolirn, and 

 P. (snigma, Dohrn,' while the third species, L. assimilans, Smith, ^ was 

 referred by Mr. E. A. Smith to Labyrinthus. The former two species 

 vyere regarded by Pilsbry "as an independent line of evolution from 

 typical Isomeria, rather than as an intermediate or ancestral form 

 between homeria and Labyrinthus ". Previously, howevei", he had 

 regarded the group intermediate between these two sections.^ Since 

 tliis group does not, in my opinion, assimilate with either section 

 named, 1 adopt his earlier view and therefore dissociate it from 

 homeria, and propose to create for its reception the genus Ambages,*' 

 taking P. vexans as the type. It differs from Isomeria in having 

 the teeth more strongly developed, and from Labyrinthus in the 

 sub-globose depressed form. 



Ambages Shaemani, n.gen. et n.sp. 



Shell umbilicate, de[)ressed orbicular, closely striated, the striae 

 broken up into rather coarse granules ; light brown. Npire sub-convex, 

 suture impressed, apex obtuse. Whorls 4f, increasing regularly, 

 slightly convex above, tumid below, penultimate whorl angulated, 

 last whorl rounded at the periphery, suddenly and shortly deflexed 

 at the mouth, slightly constricted behind the peristome, and 

 bi-scrobiculate behind the basal margin. Aperture oblique, rhomboid; 

 peristome white, expanded and reflexed, continuous ; outer margin 

 semicircular, basal margin slightly incurved, columellar margin 

 projecting over the umbilicus, parietal margin nearly straight. 

 Aperture provided with four folds, namely, two equal, short, 

 transverse, entering, convergent folds — one on the basal and one on 

 the outer margin; a third fold, close to the latter, but less elevated, 



^ Man. Conch., vol. ix, p. 94, 1894. 



= Journ. Malac, vol. vi, p. 27, pi. iv, figs. 6-8, 1897. 



' Man. Conch., vol. v, p. 157, 1889. 



■* Ambages, 'obscurity.' 



