1927] Pilsbry-Bequaert, The Aquatic Mollusks of the Belgian Congo | 227 
sinuated above, retracted or effuse at base, often expanded; inner lip calloused or 
continuous. Columellar axis encircled with a spiral fold in the middle and later whorls, 
emerging more or less on the columella (but sometimes subobsolete). The operculum 
and soft parts are unknown. 
Known from Lake Tanganyika Pe From their abundance on 
beaches it is evident that these snails live in quite shallow water, and 
they have also been dredged from as deep as 80m. So far as we know, 
only dead specimens have been taken. 
While the shells of this group recall Nematurella, Pyrgula, and 
Prososthenia by their form, size and sculpture, and Pterides by the sinu- 
ous lip, they are unique among fresh-water prosobranchs for the pyrami- 
delloid columellar fold and the palatal folds of some species. However, 
both of these structures are weak or even wanting in certain species; 
and they are wanting in the early neanic stages of all those we have 
examined. 
Pending examination of the soft parts, the taxonomic position of the 
group remains uncertain. Many and various are the opinions which 
-have been advanced. We think it will turn out to be a member of the 
superfamily Rissoaces, and possibly a subfamily of the Amnicolide. 
The genus Fascinella (Stache) of Sandberger! requires comparison 
with Syrnolopsis. It is from the Cosina Chara Beds, a Dalmatian fresh- 
water deposit of Paleocene age, carrying a considerable fauna of special 
species, the genera of part of them uncertain. Until the characters of 
Fascinella are much better known, the evidence of identity with Syr- 
nolopsis claimed by Tausch, who appears to have seen neither genus, 
remains inconclusive. | 
Key to Genera and Species of Syrnolopside 
1. Shell smooth or having spiral sculpture. Syrnolopsis E. A. Smith............ 2. 
Shell having well-developed axial ribs. Anceya Bourguignat................ 3, 
| Syrnolopsis 
2. Length 8 to 12 mm., with 9 to 12 whorls; lateral outlines of the spire straight or 
slightly convex; surface smooth; columellar fold small, weakly emerging. 
S. lacustris E. A. Smith. | 
Smaller, of 7 to 9 whorls; lateral outlines rather strongly convex; surface smooth, 
spirally lirate or carinate; columellar fold strongly emerging. 
. S. minuta Bourguignat. 
Length about 4 mm., of 8 to 9 convex whorls; slender, regularly tapering; sur- 
face smoothish or with weak spiral cords; columellar fold very weak. 
. S. gracilis Pilsbry and Bequaert. 
11871, ‘Land- und- Sisswasser-Conch. der Vorwelt,’ p. 186. See also Wenz, 1923, ‘Fossilium 
Catalogus,’ Pars 20, III, p. 8841 (in the family Cceliaxide). 
