232 CLASS ITI. GASTEROPODA. ORDER VII. PECTINIBRANCHIATA. 
inches, according to the increase of the madrepore in which it became first 
imbedded. 
The shell of Magilus may be described as being white, very solid, rolled 
into an ovate spire for three or four whorls, and then continued in a straight 
or flexuous direction, so as to form a tube varying in length according to 
circumstances ; the tube is produced at the lower part into a kind of keel 
arising from a corresponding siphon in the mantle, and the surface of the 
shell altogether is generally rough and lamellated. The operculum is 
small, horny, elliptical, and disposed in subconcentric striz. 
Example. * 
Pl. CCLXVI. Fig. 2 and 3. 
Macitus antiquus, De Montford, Conchyliologie Systématique, vol. ii. 
p. 43. pl. 42. Ritppell, Mémoire sur le Magilus antiquus, f. 1 to 5. 
Le Campulote, Guettard. 
¢ 
LEPTOCONCHUS, Riippell. 
Testa subglobosa, fragilis, translucida, longitudinaliter striata, spira de- 
pressd, subobsoleta, anfractibus regulariter convexis, ultimo ventri- 
coso, inflato; apertura concentrico-ovali, inferné subsinuata, mar- 
ginibus superné disjunctis ; columella indentata, leviter truncata ; 
labro tenui, acuto. Operculum nullum. 
Another mollusk was found by Riippell on the shores of the Red Sea 
whilst searching for Magilus, participating with the habits of that animal, 
inasmuch as it lives imbedded in the same description of madrepore. Its 
shell, however, which is of a particularly light and fragile nature, does 
not exceed the ordinary measure of growth; it differs in not having the 
margins of the aperture united, and is moreover destitute of any opercu- 
lum. It has been supposed by Rang and others, that this mollusk, which 
Riippell distinguished with the new title of Leptoconchus, is merely the 
