UK 



RISELLA-LACUNA. 265 



that on the periphery strongest and duplicate, base with a 

 nearly smooth band within the peripheral lirse, then with several 

 granular lirse round the umbilicus. Diarn. 18 mill. 



Lake Tanganyika, Africa* 



R. CYCLOSTOMA, and R. GIRAUDI, Bourg. (unfigured.) 



Lake Tanganyika* 



Genus LACUNA, Turton, 1827. 

 Section LACUNA (sensu stricto.) 



L. PUTEOLUS, Turton. PI. 50, figs. 51, 52. 



Semiglobose, slightly expanded at the base, periphery obtusely 

 angulated, rather solid, opaque, glossy ; whitish, yellowish or reddish 

 white, sometimes trifasciate, the middle band broadest ; umbilicus 

 narrow, deep. Length, 4 mill. 



Northern Europe, France, Portugal. 



L. aurieularis, Mont., L. fasciata, J. Adams, L. parva, DaCosta, 

 Helix lacuna, Mont., L. rufa, Dorset. Catal., L. Montagui, Turton, 

 L. expansa, J. Adams, L. pallidula, Meyer & Mobius, L. intermedia, 

 Locard, are all synonyms, besides the quasi-varietal names conica r 

 lactea, clausa, expansa, etc., of Jeffreys. 



L. PALLIDULA, DaCosta. PL 50, figs. 53, 53a, b, 54. 



Widely umbilicated, largely, obliquely expanded, rather thin, 

 opaque, glossy ; under the epidermis are growth lines and a few 

 spiral scratches ; pale yellowish or olivaceous yellow; whorls 3, 4, 

 rapidly increasing, the last disproportionately large, suture deeply 

 impressed. Diam. 8-9 mill. 



Northern Europe, Iceland, Greenland, Spitsbergen, New England. 



L. neritoidea, Gould (fig. 54), L. patula, Thorpe, L. Thorpeana, 

 Phil., and vars. subtriangularis, Kobelt, and albescens, Thorpe, are 

 synonyms. 



L. PORRKCTA, Carpenter. PI. 50, figs. 55, 56, 57. 



Larger than L. puteolus, with more developed spire, body whorl 

 slopingly expanded, effuse below, thinly spirally striate upon the 

 thin olivaceous yellow or light brown epidermis, sometimes with a 

 pale band under the obtusely angulated periphery. 



Length, 13 mill. 



Isl. to San Diego, CaL 



