494 MOLLUSCA SUB-KINGDOM VI 
Limnaea, Lam. (Limnaeus, auct.), (Fig. 1034). Shell so. thin as to be translucent. 
Body whorl very large ; spire acute, and moderately high. Aperture wide, oval; outer 
margin sharp. Upper Jura 
(Purbeck) to Recent ; maximum 
in Tertiary. 
Planorbis, Guettard (Figs. 
1035, 1036). Discoidal (excep- 
tionally turreted), with many 
whorls. Aperture oval to 
crescent-shaped ; outer margin 
sharp. Lias to Recent; very 

a es nine OSE profuse in the Tertiary. P. 
Limnaeus pachygaster = ws fs ae ae ; é . 
Thom. Fresh - water Planorbis cornu, Brongt. var. Man- multiformes, Bronn 8p. from the 
Miocene; Morsingen, telli, Dunker. Upper Miocene; Mun- Middle Miocene of Steinheim in 
near Ulin. dingen, Wurtemberg. 7. = z - 
; Wurtemberg, is particularly in- 
teresting on account of its extraordinary variability. The different mutations of the 
species are usually found at different horizons of the fresh-water limestone occurring 

Fic. 1036. 
Planorbis multiformis, Bronn sp. Upper Miocene fresh-water limestone; Steinheim, near Heidenheim, 
Wiirtemberg. A, var. suprema. B, var. trochiformis. Cy, var. elegans. D. var. steinheimensis, 
there, and constitute, according to Hilgendorf and Hyatt, a remarkable genealogical 
sequence. 
Tsidora, Ehr. Shell similar to that of Physa. Recent ; tropical countries. 
Family 5. Ancylidae. 
Shell limpet-shaped, conical, not spiral, or with the apex recurved. Tertiary and 
Recent. 
Ancylus, Geoffrey (Fig. 1037). Shell simply conic or with the apex slightly 
incurved. Tertiary and Recent. 
Gundlachia, Pfeiff. An accessory shell at the apex of the prin- 
cipal one. Tertiary of Mayence Basin and Recent. 
Sub-Order C. TELETREMATA. Pilsbry. 

Shell absent ; mantle covering the whole upper surface of the body. Fic. 1037. 
Male and female orifices widely separated; lung orifice and anus Ancyus Dhpamplan; 
Desh. Calcaire 
central and near the taal. Desh. 
Bete Grossier; Boursault. 
Several families of this sub-order are recognised (Vaginulidae, 
Rathowisiidae, Onchidiidae), but owing to the absence of a shell, their remains are not 
preservable in the fossil state. 
Sub-Order D. STYLOMMATOPHORA. A. Schmidt. Land Snails. 
Eyes borne on the extremities of two peduncles, which are capable of invagination ; 
a pair of short tentacles, rarely obsolete, are placed in front of them. Male and female 
genital orifices contiquous, or uniting in a common vestibule, situated at the right or 
