452 



MOLLUSC* 



SUB-KINGDOM VI 



Koninck, from the Carboniferous ; Chrysostoma, Swainson (Fig. 844), from the Jura, and 

 others, which are probably the ancestors of the Umbonidae. 



Whether the genera Teinostoma (Fig. 845) and Vitrinella, Adams, together with 

 their fossil allies from the Carboniferous onward, are rightly assigned to this group, is 



FIG. 844. 



Cli r</sostoma 

 Acmon, d'Orb. 

 sp. Middle 

 Jura ; Balin, 

 near Cracow. 



FIG. 845. 



Teinosloma rotellae- 

 formis, Desh. Calcaire 

 Grossier ; Grignon, 

 near Paris. 



FIG. 846. 



Helicoeryptus pusillus, Roein. sp. 

 Coral - Rag ; Lindeuer Berg, near 

 Hannover. 



FIG. 847. 



Adeorbis 

 Desh. 

 Meeressand) 

 Seine-et-Oise 



tricostatus, 

 (Middle 

 Auvers, 



doubtful. Helicocryptus, d'Orb. (Fig. 846), from the Jura and Cretaceous, is related to 

 Vitrinella. Cyclostrema, Marryat, comprising small, lustrous shells ; and the spirally 

 striated ones known as Adeorbis, S. Wood. (Fig. 847), present strong resemblances to the 

 Umboniidae ; but, according to Fischer, they form separate families. Both of the last- 

 named genera have fossil representatives in the Tertiary. 



Family 13. Neritopsidae. Fischer. 



Shell oval to semi-globose, with short, sometimes laterally twisted spire, and without 



umbilicus or nacreous layer. Body whorl very large; aperture oval or semi-circular. 



Inner lip callous, curved, and occasionally notched. Operculum calcar- 



%eous, not spiral, with sub-central nucleus, and internally with callous 

 columellar margin, which forms a broad, angular, or rounded process 

 in the middle. Devonian to Recent. 



The Neritopsidae are distinguished from the closely related 

 Neritidae, principally by the totally different, non-spiral operculum, 

 and by the fact that the earlier whorls are not resorbed, as in the 

 Keuper ; St. Cassiaii. latter family. Detached opercula have been described under the 



names of Peltarion, Scaphanidia, Cyclidia, and Rhynchidia. 

 Naticopsis, M'Coy (Neritomopsis, Waagen), (Figs. 848-850). Shell oval to globose, 



FIG. 848. 



Naticopsis Mandel- 

 slohi, Klipst. sp. 



Fio. 849. 



A, Naticopsis ampliata, Ph,l. Carboniferous ; Vise, Belgium. 

 Ji, Operculum of N. pianispira, from same locality (after de 

 Koninck). 



FIG. 850. 



Naticopsis lemniscata, Hoernes. Trias ; 

 Esino, Lombardy. Original coloration 

 preserved. 



smooth or transversely striated. Aperture oval ; inner lip flattened, somewhat 



