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 Eecent ; maximum 

 in Tertiary. 



Planorbis, 

 1035, 1036). 

 tionally 

 whorls. 



Fio. 1034. 



Limnaeus pachygaster, 

 Thoin. Fresh - water 

 Miocene ; Morsingen, 

 near Ulin. 



Guettard (Figs. 

 Discoidal (excep- 

 turreted), with many 

 Aperture oval to 

 crescent -shaped ; outer margin 

 sharp. Lias to Recent; very 

 profuse in the Tertiary. P. 

 multiformis, Bronn sp., from the 

 Middle Miocene of Steinheim in 

 Wurtemberg, is particularly in- 

 teresting 011 account of its extraordinary variability. The different mutations of the 

 species are usually found at different horizons of the fresh-water limestone occurring 



FIG. 1035. 



Planorbis cornu, Brongt. var. 

 telli, Bunker. Upper Miocene ; 

 dingen, Wurtemberg. 



Man- 



Mun- 



FIG. 1036. 



Planorbis multiformis, Bronn sp. Upper Miocene fresh -\vater limestone; Steinheim, near Heidenheim, 

 Wiirtemberg. A, var. supremn. B, var. trochiformis. C, var. elegans. D. var. steinheimensis. 



there, and constitute, according to Hilgendorf and Hyatt, a remarkable genealogical 

 sequence. 



Isidora, Ehr. Shell similar to that of Phijsa. 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. FIQ 1Q3 ., 

 Male and female orifices widely separated; lung orifice and anus Ancylus Dutemplei, 

 ventral and near the tail. Desh. Caicaire 



Grossier; Boursaiut. 



Several families of this sub -order are recognised (Vaginulidae, 

 Rathouisiidae, 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. 



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 contiguous, or uniting in a common vestibule, situated at the right or 



