466 



MOLLUSQA 



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 

 Eecent. 



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. 



FIG. 914. 



Vermetus (Thylacodes) arenarius, Linn. 

 Miocene ; Grund, near Vienna. 1/2- 



FIG. 015. 



Petaloconchus intortus, Lain 

 Pliocene ; Montespertoli, near 

 Florence. Some of the tubes are 

 fractured, and show the internal 

 lamellae. 



FIG. 910. 



Siliquaria, striata 

 Desh. Calcaire Grossier; 

 Chaussy, near Paris. 



Sub-genera : Thylacodes, Guettard (Fig. 914) ; Petaloconchus, Lea (Fig. 915). 

 Recent. 



Tertiary and 



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. TJie 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. 



