THE GASTROPODA 155 
mantle slit in the female only (Fig. 45); pedal tentacles elongate. Siliquaria, 
Bruguitre ; mantle and shell slit in both sexes for the whole length of 
the branchial cavity ; pedal tentacles rudimentary. Faminy 30. CArcrIDAr, 
Gray. Shell almost completely uncoiled in one plane, and furnished with 
internal septa; aperture circular. Genus—Caecum, Fleming (Fig. 68) ; 
British. Famity 31, Turrirecnipar, Clark. Shell very long with 
numerous whorls ; head large and prominent ; mantle border fringed ; 
no siphon; foot broad and truncated. Genera—Turritella, Lamarck ; 
British. MJesalia, Gray. Mathilda, Semper; the summit of the shell 
hyperstrophic. Famity 32. SrRuTHIOLARIIDAE, 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. Famity 34. SrrompBrpa®, Gray. Foot narrow, arcuate, 
compressed laterally, without ventral sole (Fig. 75, f) ; 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. Famity 35. XENOPHORIDAR, 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. Hotrochus, Whitfield ; 
from the Silurian. Fairy 36. Capuntpan, 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. 
Famity 37. Hirronycrpar, Fischer. Visceral mass and shell conical ; 
foot feebly muscular, capable of secreting a ventral calcareous plate ; 
animal fixed. Genera—Hipponyx, Defrance. Mitrularia, Schumacher ; 
the shell with an internal appendage shaped like a half-horn. Faminy 38. 
CALYPTRAEIDAR, Broderip. Visceral mass spiral; shell flattened, with 
a short spire; lateral cervical lobes present ; foot short and circular ; 
accessory genital glands present. Genera—Culyptraca, 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). Fairy 39. Naricipar, Recluz. Foot divided into two, the 
posterior half bearing the operculum ; a wide epipodial velum ; tentacles 
flattened ; snout elongate; shell turbinated. Genus—Narica, Recluz. 
Faminy 40. Naticipan, Swainson. Foot highly developed and provided 
