MACLUREIDyE. 11 



Genus PILEOLUS (Cookson), Sowerby. 1823. 



Shell limpet-like, solid, circular or elliptical at the base, convex, 

 with subcentral, non-spiral apex; a])erture small, semilunar; col- 

 umellar septum convex, smooth or toothed, peritreme continuous. 

 Operculum unknown. Fossil; Jurassic to Cretaceous. P. plica- 

 Tus, Sowb. 



Subgenus Gargania, Guiscardi. 1856. 



Apex elevated, inclined backwards beyond the peritreme, surface 

 radiately ribbed ; lij^ with a central, internal depression. Creta- 

 ceous. G. Brocchii, Guiscardi. 



Family MACLUREIDM 



Shell discoidal, few whorled, longitudinally grooved at the back, 

 and slightly rugose with growth-lines ; dextral side convex, deeply 

 and narrowly perforated, sinistral side flat, exposing the inner 

 whorls. Operculum calcareous, solid, sinistrally subspiral, with 

 two internal apophyses, one of them beneath the nucleus, very thick 

 and rugose. 



Genus MACLUREA, Lesueur, em. 1818. 



The characters are those of the family, of which this is the sole 

 genus. A dozen palaeozoic sj)ecies from North America and Scotland 

 have been described. M. Logani, Salter. (Struct, and Syst. Conch., 

 t. 82, f. 8, 9) ; M. magna, Lesueur. (Ibid, t. 65, f. 10). 



Conchologists have been at a loss where to place this singular 

 genus ; according to some it has been included in Solariidse ; others 

 have placed it in Pleurotomariidse and in Atlantidi?e. In my "Struc- 

 tural and Systematic Conchology" I have given it a position be- 

 tween Bellerophontidie and Haliotidie. I think that Dr. Fischer's 

 removal of the group to the vicinity of Neritidte, on account of the 

 apophyses of the operculum, is a happy idea of that learned con- 

 chologist. 



