346 PROF. EHRENBERG ON ANIMALS OF THE CHALK 
forms with five and six rays, which approach very near to Dic- — 
tyocha Stella of the chalk marl of Caltanisetta, and together 
with this species form a distinct group in the genus Dictyocha, 
whose radiate skeleton of siliceous bars is not reticulately ana-_ 
stomosed. These two new species are, Dictyocha (Actiniscus) 
Sirius with six longish rays, and D. (Ac.) Pentasterias with five 
rays. Unfortunately, the greater number of these forms, from 
having been sent by way of Stockholm, as opportunity offered, and 
not having come to hand till six months afterwards, were dead 
when they arrived, and some few only still retained life and mo- 
tion ; yet even in the dead shells there could generally be detected, — 
although altered in form, distinct remains of the ovaries and ; 
other organic details, which distinguished them very accurately | 
from any fossil remains accidentally mixed with the mud. 
From the memoir read on the 27th of July, it appeared that 
in the Peruvian and Mexican sea-water microscopic organisms 
are also met with still in a living state, which are partly identical 
with species from the chalk marls, and partly illustrate a hitherto 
obscure form occurring in them, namely by claiming for the pre- 
sent world an apparently extinct genus peculiar to the chalk. 
This latter form was found on an alga at Callao, which Du 
Petit Thouars brought thence to Paris, and which Dr. Montagne 
had named Polysiphonia dendroidea, together with Podosira 
moniliformis. It had completely the zigzag and at the same time 
riband-like form of Tabellaria vulgaris (Bacillaria tabellaris), 
but was neatly divided in the interior by two curved septa in 
the longitudinal direction of each individual bar into three cham- 
bers. A very similar form, but as a single bar, was noticed in 
the Memoir on the Masses of existing siliceous Infusoria, 1837, 
as Navicula africana of the chalk marl from Oran, and more 
accurately described in the Memoir on the Formation of Chalk 
in 1838*. In this fossil state it had, however, as stated, always 
presented itself merely as single bars, whose form and large’ 
central aperture brought them nearest to the genus Navicula. 
In the living form from Peru it might be seen, even in the dried 
and remoistened state, that several such bars are connected to- 
gether in the form of zigzag incised gaping bands, and that the 
curved lines in the interior of the individual bars were essential 
parts of the organization, as three green and granular inner sacs, 
=—s 
[* Full abstracts of these Memoirs by T. Weaver, Esq., were published in 
the Philosophical Magazine, Nos. 118 and 119; and in the Annals of Nat. 
History, vol. vii. p. 296.—Eb.] 
