CLASS IV 



GASTROPODA 



539 



Superfamily 3. TAENIOGLOSSA Bouvier. 



Teeth of the radula seven in each transverse row. Mainly holostomate forms, but 

 some genera have deeply notched apertures, as in the higher divisions. 



Family 1. Purpurinidae Zittel. 



Thick-shelled, oval, unth platform-like spire, and with- 

 out pearly layer, TVliorls flcottened beneath the suture and 

 angular, the angles often beset loith nodes. Body whorl 

 large ; aperture oval, with anterior emargination, and 

 discontinuous peristome. Operculum unknoion. Carboni- 

 ferous to Cretaceous. 



Trachydomia Meek and Worth. {Trachijnerita Kittl). 

 Coal Measures ; North America and Europe. Pseudoscalites 

 Kittl ; Tretospira Koken. Trias ; Europe. 



Purpurina d'Orb. Elongate-oval. Whorls angular 

 superiorly, spirally ribljed, with transverse folds or costae, 

 highly ornamented, often with umbilical fissure. Aperture 

 oval, anteriorly notched. Rhaetic and Jura. 



Purpuroidea Lycett (Fig. 924). Spire with successive 

 steps or platforms, the flattened surface beneath the suture 

 bounded by a row of n6des. Last whorl inflated, smooth, 

 canal-like notch ; outer lip thin. Jura and Cretaceous. 



Brachytrcma Morris and Lycett ; Tomocheilus Gemm. 



Fig. 924. 



Pur}mroidea nodulata (Young 

 and Bird). Great Oolite ; Minchin- 

 hampton, England. 



Aperture anteriorly with 



Jura. 



Family 2. Littorinidae Gray. 



Shell turbinate, usually smooth or spirally ornamented, without nacreous layer. 

 Aperture rounded ; outer lip sharp. Operculum horny, pa,ucispiral. Marine. 

 Ordovician to Recent. 



Fossil shells 



of this family are distinguished solely from those of the Turbinidae 

 and Trochidae by the absence of a pearly layer. The animal, 

 however, differs radically. The heart has but one auricle in 

 the Littorinidae, two in the Turbinidae and Trochidae. The 

 radula in the last-named groujis is rhipidoglossate ; in the 

 present family it is taenioglossate. The differences in essential 

 structure are thus seen to be considerable ; yet the shells 

 when fossilised are so similar, it can scarcely be doubted that 

 the so-called Paleozoic Littorinidae are in many cases very 

 closely related to genera referred to the Turbinidae and 

 Trochidae. The limits of these families are therefore very 



Fk;. 92o. 



uncertain, so far as Paleozoic forms are concerned. Among 



Turho7iUella subcostata 

 (Goldf.). Middle Devonian ; 

 Paffrath, near Cologne. 



the extinct genera which exhibit great similarity to Littorina, 

 but are often assigned to the above-named families, may be 

 mentioned the following : Holopea Hall. Ordovician to 



Devonian. Turbonitella de Koninck (Fig. 925). Devonian and Carboniferous. 



Portlockia, Turbinilopsis and Ehabdopleura de Koninck. Lower Carbonifei'ous. 



Lacunina Kittl. Trias. 



Littorina Fer. (Fig. 926). Thick-shelled, turbinate to globose, smooth or spirally 



striated, without umbilicus. Aperture oval. Jura to Recent. 



