THE GASTROPODA 155 



mantle slit in the female only (Fig. 45) ; pedal tentacles elongate. Siliquaria, 

 Bruguiere ; mantle and shell slit in both sexes for the whole length of 

 the branchial cavity ; pedal tentacles rudimentary. FAMILY 30. CAECIDAE, 

 Gray. Shell almost completely uncoiled in one plane, and furnished with 

 internal septa ; aperture circular. Genus Caecum, Fleming (Fig. 68) ; 

 British. FAMILY 31. TURRITELLIDAE, Clark. Shell very long with 

 numerous whorls ; head large and prominent ; mantle border fringed ; 

 no siphon ; foot broad and truncated. Genera Turritella, Lamarck ; 

 British. Jfesalia, Gray. Mathilda, Semper ; the summit of the shell 

 hyperstrophic. FAMILY 32. STRUTHIOLARIIDAE, Fischer. Spire of shell 

 conical ; aperture pointed and subcanaliculated anteriorly ; foot oval, 

 rather small ; head elongate with short tentacles ; siphon very slightly 

 developed. Genus Struthiolaria, Lamarck. FAMILY 33. CHENOPODIDAE, 

 Fischer. Spire of shell elongated ; margin of aperture expanded ; foot 

 elongated and narrow ; snout short ; tentacles long ; siphon very short. 

 Genera Chenopus, Philippi ; British. Alaria, Morris and Lycett 

 Jurassic and Cretaceous. Spinigera, d'Orbigny ; Jurassic. Diartema, 

 Piette ; Jurassic. FAMILY 34. STHOMBIDAE, Gray. Foot narrow, arcuate, 

 compressed laterally, without ventral sole (Fig. 75, /) ; snout long ; ocular 

 peduncles longer and stouter than the tentacles. Genera Strombus, Lin- 

 naeus ; shell ovoid, with elongated aperture ; mantle border and aperture 

 of shell not digitate. Pteroceras, Linnaeus ; mantle border and aperture of 

 shell digitate. Rostellaria, Lamarck ; spire of shell elongate ; aperture 

 prolonged anteriorly into a canal and laterally into an aliform expansion 

 (Fig. 46). Terebellum, Klein ; shell elongated with a short spire ; tentacles 

 aborted. FAMILY 35. XENOPHORIDAE, Philippi. Snout elongated ; foot 

 divided transversely into two parts, the posterior part bearing the oper- 

 culum ; shell conical, carinated. Genera Xenophorus, Fischer (Fig. 134) ; 

 with foreign substances agglutinated on the shell. Eotrochus, Whitfield ; 

 from the Silurian. FAMILY 36. CAPULIDAE, Fleming. Visceral sac and 

 shell conical, but slightly incurved posteriorly; a tongue-shaped projection 

 between snout and foot ; columellar muscle horseshoe-shaped. Genera 

 Capulus, Montfort. Thyca, Adams ; parasitic on Asterids ; without a radula ; 

 foot rudimentary. Platyceras, Conrad ; from the Silurian onwards. 

 FAMILY 37. HIPPONYCIDAE, Fischer. Visceral mass and shell conical ; 

 foot feebly muscular, capable of secreting a ventral calcareous plate ; 

 animal fixed. Genera Hipponyx, Dei'rance. Mitrularia, Schumacher ; 

 the shell with an internal appendage shaped like a half-horn. FAMILY 38. 

 CALYPTRAEIDAE, Broderip. Visceral mass spiral ; shell flattened, with 

 a short spire ; lateral cervical lobes present ; foot short and circular ; 

 accessory genital glands present. Genera Calyptraea, Lamarck ; shell 

 spiral, with central summit and circular aperture ; British. Crepidula, 

 Lamarck ; shell oval, with nearly obsolete spire and marginal summit, 

 furnished with an internal horizontal posterior septum. Crucibulum, 

 Schumacher ; shell conical, with an internal corniform appendage (Fig. 

 69). FAMILY 39. NARICIDAE, Recluz. Foot divided into two, the 

 posterior half bearing the operculum ; a wide epipodial velum ; tentacles 

 flattened ; snout elongate ; shell turbinated. Genus Narica, Recluz. 

 FAMILY 40. NATICIDAE, Swainson. Foot highly developed and provided 



