466 MOLLUSCA SUB-KINGDOM VI 
Aperture oval, with faint canal; outer lip with anterior and median emargination. 
Abundant in the Cretaceous. 
Family 13. Vermetidae. Adams. 
Shell tubular, the earlier whorls spiral, the later ones irregularly twisted, free or 
attached. Aperture round; operculum horny, sometimes wanting. Carboniferous to 
Recent. 
Some fossil Vermetidae are liable to be mistaken for Serpulidae, but differ from 
them nevertheless in the structure of 
the shell and spiral nucleus. The 
determination of the few Palaeozoic 
and Mesozoic forms is uncertain. 
Vermetus, Adans. (Figs. 914, 915). 
Shell usually attached, irregularly 
tubular, internally vitreous, and often 
with septa. Carboniferous (?) to Recent. 
Abundant in the Tertiary. 






Fic. 915. 

Petaloconchus <intortus, Lamy: Fic. 916 
Fic. 914 Pliocene ; Montespertoli, near us a eae 
i Oia Florence. Some of the tubes are Siliquaria striata 
Vermetus (Lhylacodes) wrenarius, Linn. fractured, and show the internal Desh. Calcaire Grossier; 
Miocene ; Grund, near Vienna. 1/s. lamellae. Chaussy, near Paris. 
Sub-genera: Zhylacodes, Guettard (Fig. 914); Petaloconchus, Lea (Fig. 915). Tertiary and 
Recent. 
Siliquaria, Brug. (Fig. 916). Shell free, coiled in a loose spiral. Aperture lateral, 
and with a slit which continues as a fine cleft or row of pores throughout the entire 
length of the shell. Cretaceous to Recent. 
Family 14. Caecidae. Adams. 
Shell small, discoidal in early stages, later becoming tubular. The decollated nucleus 
replaced by a septum. Operculum round, horny. Tertiary and Recent. 
Caecum, Flem. About one hundred Recent and twenty Tertiary species are known. 
’ ‘ 
Family 15. Melaniidae. (Lamarck) Gray. 
Shell turreted to oval, with thick, dark-coloured epidermis. Apex usually truncated 
and corroded. Aperture oval, sometimes canaliculate. Operculum horny, spiral. Jura 
to Recent. 
