Notes on Kenya land and freshwater snails. 10. Variation in the Gulella ugandensis complex (Streptaxidae)

Gulella ugandensis (E.A. Smith, 1901) was described under Ennea from material collected in Kenya at the terminus of the Uganda Railway by Doherty between September 1900 and April 1901. At that time much of what is now western Kenya was included in Uganda, hence the specific epithet. Later some very similar shells were named Ennea optata by Preston (1911). These had been collected on Mt. Kenya at 6000-8000 ft; the same author later (Preston, 1913) also described a var. obesa and a var. majuscula based on material from the Kenangop, Aberdare Mts. Gulella ugandensis s.l. is a common and characteristic component of the molluscan fauna of the Kenya highlands, easily recognised by the rather large, mostly smooth shell and, usually, a dental formula 1:3:1:1(2). As I have already pointed out (Verdcourt, 1962) there are difficulties concerning the circumscription of this species. There is variation in both sculpture and dentition and, in some lots, there are shells closely resembling G. sellae (Pollonera, 1906) which typically is more cylindrical, much more strongly striate and has the columellar process simple, not bifid, although the rest of the dentition is very similar to that of G. ugandensis. Comparing typical specimens of the two species one would not suspect there could ever be any difficulty in separating them. Examination of a range of material from many different localities shows that the difficulty is real enough. My attention was drawn again to the problem when Mr. loan Thomas of Oundle School, who accompanied a Brathay Exploration Group expedition to the Cherangani Hills in Kenya, collected a reasonable sample of a well-marked variant of this complex. Apart from this, Dr. W. Adam (1965) has recently described from four shells what he believes is a species distinct from G. ugandensis and it is also evident that he believes G. optata is yet another species. I doubt if he saw very much material. Little but the type material is available in the British Museum (Natural History)¹ and other European museums. I therefore, through the kindness of the curator, borrowed from the National Museum, Nairobi, the material of the group, mainly comprising series of specimens I had presented to that museum between 1952 and 1964. Although still inadequate to solve the problem involved, it has thrown some light on the matter; the facts tabulated below should deter anyone from erecting new species in this group too hastily.