CLASS IV GASTROPODA 575 



many whorls. Aperture oval to crescent-shaped ; outer margin sharp. Lias to 



Recent ; very profuse in the Tertiary. P. multiformis (Bronn), from the Middle 



A n c D 



Fig. 1085. 



Planorbis multiformis (Bronn). Upper Miocene fresh-water limestone ; Steinheim, near Heidenheini, 

 Wtirteniberg. A, var. suprema. B, var. trorJiiformis. C, var. chgans. D, var. steinheiviensin. 



Miocene of Steinheim in Wiirtemberg, is particularly interesting on account of its 

 extraordinary variability. The different mutations of the species are usually found 

 at different horizons of the fresh-water limestone occurring there, and constitute, 

 according to Hilgendorf and Hyatt, a remarkable genealogical sequence. 



Isidora Ehr. Shell similai' to that of Physa. Recent ; trojaical countries. 



Family 5. Ancylidae Dall. 



Shell limpet-shaped, conical, not spiral, or ivith the apex recurved. Tertiary and 

 Recent. 



Ancylus Geoffrey (Fig. 1086). Shell simply conical or with the apex slightly 

 incurved. Tertiary and Recent. 



Gundlachia Pfeiff. A partial septum is developed at the end of 

 the first season's growth. Tertiary of Mayence Basin and Recent. 



Suborder C. TELETREMATA Pilsbry. 



Shell absent ; mantle coverincj the whole upper surface of the body. 

 Male and female orifices widely separated; lung orifice and anus Fki. losti. 



ventral and near the tail. Desr^ciliJ^^G^^ 



Several families of this suborder are recognised (Vaginulidae, 

 Rathouisiidae, Onchidiidae), but owing to the absence of a shell, tlieir remains are 

 not preservable in the fossil state. 



Suborder D. STYLOMMATOPHORA A. Schmidt. Land Snails. 



Eijes borne on the extremities of two peduncles, which are capable of invagination ; 

 a fair 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 

 left side of the head. Buccal retractors present ; lung foramen and anus anterior to the 

 end of the foot, not ventral. 



This suborder comprises most recent and all fossil land snails, and is divisible 

 into series or superfamily groups. The families proper are based almost wholly upon 

 characters of the soft anatomy, which are herein largely omitted or abridged. 



Superfamily 1. HOLOPODA Pilsbry. 



No longitudinal grooves above the margins of the foot ; jaw present, teeth quadrate. 



Family 1. Helicidae Keferstein. Helices. 

 Shell depressed, globose or oval and elevated. Tertiary and Recent. 



This comprises an enormous assemblage in the Recent fauna, but most of the genera 

 have not as yet been found fossil. All the typical forms will probably in time be 



