VERMETIDA. I27 
irregularly twisted, carinated. Operculum large, smooth, circu- 
lar, concave; the scar of attachment central, rugose. 23 sp. 
World-wide. M. Rougemont has observed at Naples that the 
S. maximum (1xvii, 74) emits from its mouth a thin veil-like 
plaited substance, which entangles small natatory animals, and 
is subsequently withdrawn. 
VERMETUS, Adanson. (Macrophragma, Carp. Aletes, Carp.) 
Shell mostly spirally twisted, affixed, usually decussated, colu- 
mella folded. Operculum thin, concave, scarcely spiral. The 
Vermetus of most authors is the Vermiculus of Lister. 27 sp. 
Widely diffused. V. carinatus, Quoy (1xvii, 75). 
PETALOCONCHUS, Lea. An American tertiary fossil. Shell with 
two internal ridges running spirally along the columella, becoming 
obsolete near the apex and aperture. V. sculpturatus, Lea 
(Ixvii, 76). 
THYLACODES, Guettard. (Serpulorbis, Sassi. Lementina, Gray. 
Hatina, Gray. Cellularia, Schmidt. Cladopoma, Gray. Tetra- 
nemia, Morch.) Shell tubular, irregularly twisted, adherent, 
aperture rounded, columella not plicate. No operculum, or 
minute when present. The animal has a truncated foot, pro- 
duced in front into tentacular processes. Many living and 
several tertiary species; and one cret.; India. 7’. arenaria, Quoy 
Chev e TYy: 
BIVONIA, Gray. Shell affixed, mostly spiral,aperture contracted, 
circular, with spiral, interruptedly nodulose lire, and a median 
elevated line ; columella smooth. Operculum small, rudimentary. 
Animal with cylindrical tentacles, pedal filaments subulate or 
setaceous. Tsp. B. triquetra, Bivona (Ixvii. 80). When the shells 
are not perfect with the margin of the aperture, they are very 
difficult to distinguish from Spiroglyphus. 
SPIROGLYPHUS, Daudin. Animal forming a groove on the 
surface of shells or stones, covering it over with shelly matter, 
and forming a tubular case. Many zoologists consider the 
Spiroglyphus to be an annulose animal allied to Serpula, but of 
this there is no positive proof. ‘he young animal, when first 
hatched, is covered with an ovate, regular shell, consisting of a 
whorl and a half; it soon attaches itself to the surface of some 
stone or other shell, in which it forms a canal, at first shallow, 
but afterwards deeper. 8S. spirorbis, Dillw. (Ixvii, 78). 
SILIQuARIA, Brug. 
Etym.—Siliqua,a pod. Syn.—Tenagodus, Guettard. 
Distr.—15 sp. Mediterranean, Australia. Fossil,20 sp. Ter- 
tiary. The typical species, as well as several others, occur 
imbedded in sponges. S. anguina, Linn. (Ixvii, 79). 
Shell tubular; spiral at first, afterwards irregular; tube with 
a continuous longitudinal slit. Opereulum spiral, like that of 
