XIV MONOTOCARDIA TAENIOGLOSSA 4II 



Sub-order II. Monotocardia. — Heart with one auricle, one 

 cteuidium (the left), monopectinate, fused with the mantle 

 (except in Valvata), one kidney, not receiving the genital 

 products, nervous system somewhat concentrated, proboscis and 

 penis usually present. 



{a) Ptenoglossa. — Radula with formula 00. o. co, teeth 

 similar throughout, outermost largest (p. 224). 



Fam. 1. lanthinidae. — Snout prominent, blunt, no eyes, shell 

 helicoid, fragile, bluish, no operculum ; eggs carried on a raft of 

 vesicles attached to the foot (Fig. 42, p. 126). Pelagic only. 

 Pliocene . Genera : lanthina, Recluzia. 



Fam. 2. Scalariidae. — Shell long, turriculate, whorls often 

 partly uncoiled, with longitudinal ribs and prominent lamellae, 

 aperture circular, operculum spiral, corneovis, animal carnivorous. 



Ordovician . Principal genera ; Scalaria, Eglisia, Elas- 



moneura (Silurian), Holopella (Silurian to Trias), Aclis. 



(h) TAENIOGLOSSA. — Eadula with normal formula 2.1.1.1.2, 

 marginals sometimes multiplied (p. 223). 



Section I. Platypoda. — Foot more or less flattened ventrally. 

 Fam. 1, Naticidae. — 'Foot very large, produced before and 

 behind, propodium reflected upon the head, eyes absent or buried 

 in the integument, central and lateral tooth of the radula tri- 

 cuspid, middle cusp strong ; shell globular or auriform, outer lip 

 simple, operculum corneous or calcareous, nucleus excentrical. 



Carboniferous . Principal genera; Natica, with many 



sub-genera ; Ampidlina (Tertiary) ; Amaura ; Deshayesia (Ter- 

 tiary) ; Sigaretus (Fig. 91, p. 186), shell auriform, last whorl very 

 large, operculum much too small for the aperture. 



Fam. 2. Lamellariidae. — Mantle reflected over more or less 

 of the shell, shell delicate, no operculum. Eocene . Prin- 



cipal genera : Lamellaria, shell completely internal, transparent, 

 auriform ; some species deposit their eggs on compound Ascidians 

 (p. 74) ; Velutina, shell almost entirely external, paucispiral, 

 with a thick periostracum ; Marsenina, shell auriform, partly 

 internal ; Onchidiopsis, shell a membranous plate, internal. 



Fam. 3. Trichotropidae. — Branchial siphon short, eyes on 

 the outer side of the tentacles ; radula closely allied to that of 

 Velutina; shell conical, last whorl rather large, periostracum 

 thick and hairy, operculum blunt claw-shaped, nucleus terminal. 

 Cretaceous . Genera : Trichotropis, Torellia. 



