24.6 | CRETACEOUS GASTROPODA 
H. and A. Adams accept two genera Onustus, Humphrey, and Xenophora, 
Fisher (Phorus, Montfort). : 
Mr. Deshayes remarks, that the distinctions could be kept up between the 
living, but not between the fossil species, and, in rejecting the first name as of no 
sufficient authority, he retains only the second one. We would not attribute very 
sreat importance to the existence or want of an umbilicus, but the thin, anterior 
margin of the whorls, often provided with hollow spines or tubes, and the concave 
basis, seem to us useful distinctive characters of Onustus; and as these distinctions 
appear to be supported by some others, in the animal and operculum, the separation 
into two genera may be regarded as rather convenient. Deslongchamps apparently 
restricts the name Onustus only to those species, which do not accumulate any 
foreign objects on the exterior of their shells, (vide Bull. Soc. Linn. Norm., Caen, 
Vol. VI, 1862, p. 147). Ht is true, that the fossil and recent species of Onustus 
do not accumulate these foreign masses in such great quantities, as usually the 
AXenophore do, and that in some fossil species of Onustus, no impressions are known 
on theshell. Still it does not appear probable, that such forms could be generically 
separated on account of this sole peculiarity. Moreover it would be advisable to 
compare some of those species with Infundibulum and Galerus of the Caryrrripa, 
which they very much resemble. 
The Oyusrip# are mostly inhabitants of the eastern tropical seas; they 
are said to prefer-deep waters and stony or gravelly ground to shallow waters. 
At present there are only about 20 living species known, and about as many 
tertiary ones. Of cretaceous species there are enumerated by Pictet and Campiche, 
under the name Phorus, (Mat. p. 1. Pal. Suisse., 3me. Ser., Foss. Ste. Croix., 
p- 536), five European and two American. Of the former, Phorus minutus, Zek., 
must be excluded, being only a young specimen of Astraliwm radiatum, Zek., 
sp. (vide Stoliczka in Sitz. Akad., Wien, 1865, Vol. LIT, Revision, etc., p. 59). 
Binkhorst (Gast. et. Ceph. Limbeg., 1861, p. 38, pl. 3, fig. 14), described and 
figured again the Yenophora onusta, (Trochus id of Nilson, Hiesinger, Goldfuss and 
J. Miller). The Ph. wnbilicatus, Tuomey, is considered by Gabb, in his Synopsis 
of cretaceous fossils, as doubtful. We have obtained from the uppermost beds 
of the South Indian cretaceous deposits only one specimen of a new Xenophora. 
The jurassic and liassiec deposits of Europe have ‘yielded some ten species, belong- 
ing chiefly to Onustus. Deslongchamps also described a Phorus ( ? Xenophora) 
Bouchardi, from the upper devonian beds of the Boulonais, (Bull. Soc. Linn. 
Norm., Caen, 1862, Vol. VI, p. 151, pl. 8). 
