Monthly Microscopicall 
Journal, Feb. 1, 1869. J 
North Atlantic Deposits. 
107 
dead in the deposits —interpose an awkward difficulty in tlie way 
of those who argue that the present geological period is, in every 
respect, a continuation of the cretaceous period of the past. 
The only organism possessing a siliceous shell analogous to the 
first genus of those I am about to describe, of which I can find any 
published record, is one which v/as discovered by the late Professor 
Bailey, of New York, and described by him in ' The American 
Journal of Science and Art' for July, 1856, in a paper "On 
Microscopic Forms found in the Soundings of the Sea of Kam- 
schatka." Under the head "Infusoria Ehizopoda," and amongst 
Diatomacese, Polycystina, and " Zoolitharia," Professor Bailey thus 
characterizes the form alluded to : — - 
" Cadium : nov, gen. Animal unknown (a Ehizopod ?) ; shell, 
siliceous ! ovoidal, with a bent beak and circular aperture." " Cadium 
marinum: shell with numerous meridian lines, of which about 
twelve are visible at once ; length, 2 ™ ; diameter, 1 I propose 
the genus Cadium to include some small shells whose siliceous 
structure I have fully proved, and which occur in the above-men- 
tioned soundings as well as m the Gulf Stream. In the specimen 
figured, from 10 to 12 longitudinal striae were seen at once on the 
upper surface of the shell ; but in some specimens from the Gulf 
Stream the striae were twice as numerous." 
On comparing Fig. 5 of the Plate accompanying this paper with 
Fig. 1, which is copied from Professor Bailey's drawing of Cadium 
marinum, it will be seen that these two forms are generically and 
in all probability specifically identical, although difiering from each 
other in some minor details, such as the size and degree of curva- 
ture of the " beak," the number of the meridional grooves, and the 
absence in Bailey's specimens of the minute tubercular process at 
the posterior part of the shell, which, in some of the North Atlantic 
forms, becomes developed into a remarkable caudiform appendage. 
There exists, however, another Oceanic Ehizopod to which the 
Atlantic forms of Cadium seem to bear a very close resemblance ; 
namely, Lagynis. This Ehizopod, which was first observed by 
Schultze in 1849 in the surface-waters of the Baltic, was described 
and figured in his work, ' TJeber den Organismus den PolythalamienJ 
published at Leipzig in 1854. The shell of Lagynis, however, is 
described as being not siliceous, but chitinoid ; and in this respect it 
difiers from the shell of Cadium. Yet the general outline is so 
similar, and — what is of more importance — the general appearance 
and arrangement of the animal body, as seen whilst retained within 
the cavity of the shell, is of so peculiar and so similar a character in 
the two forms, that the question at once arises whether the presence 
in one shell of the siliceous ingredient, and its entire or partial 
absence in the other, may not, after all, be due to local conditions 
depending on habitat rather than to any inherent idiosyncrasy in 
