THE CYPRIS AND ITS FOSSIL ANCESTORS. 83 

Lingula flags, wherein it rejoices under the name of Primitia 
Solvensis, and from the assemblage of fossils found with it—is also 
undoubtedly marine. 
Ascending into the Silurian formation we no sooner enter into 
its lowest or basement beds than we are confronted with its first 
appearance under a new name—that of Beyrichia. The rocks, in 
which this probably modified form appears are the Arenig rocks of 
North and South Wales. 
And now we find that, whereas we had hitherto met with but 
one species at a time, namely: first, Primitia, and afterwards 
Beyrichia ; at the top of this Arenig formation the two species 
now exist conjointly. 
At the top of the Lower Silurian we come to indications fhat 
the Ostracodean ancestors of the Cypris had undergone material 
development in point of species, because we find them represented 
by the forms of Leperditia, Beyrichia, Cythere, and frimitia, 
all of which forms have been carefully and skilfully worked 
out by Prof. Rupert Jones, to whose labours we are much indebted 
for the knowledge we possess upon the Ostracods of the Lower 
Palzeozoic rocks. 
We now make a great rise in these ancient rocks, and pass with 
one bound from the Lower Silurian to the middle of the Upper 
Silurian, namely, the Wenlock group. Here some new genera and 
species come in, namely, the Cytherellina, Primitia excavatt, 
Primitia lenticularis, and Cythere Grindrodiana, and especially 
Beyrichia Kledena, which is conspicuously present in the Downton 
beds. Itis stated by Mr. Etheridge that no less than twelve.species 
of Primitia, besides other Ostracoda, have been determined in these 
rocks by Prof. Rupert Jones. 
The next group of rocks, namely the Ludlow, at the top of the 
Upper Silurian formation, witness the coming in of four new 
genera of Ostracoda,—viz., Cypridina, Entomis, Kirhbya, and 
Moorea,—and here we may note that in the Cypridina we begin 
to have the, so to speak, more direct lineal descent of the Cypris. 
The forms of the Ludlow formations pass into that of the Downton 
sandstone before alluded to. From the lithological appearance of 
this rock, as observed at Ludlow, we should say that, although all 
these forms are marine, the presence of Beyrichia Kledena in the 
fine light-coloured sandstone indicates a shallowing sea, and that 
they were entombed not far from a coast line. 
In the Devonian, the Ostracoda holds its position in full force, 
but as no new genera or species come in, we may pass up to the 
next formation, the Carboniferous, where we find the Ostracoda 
represented by 130 genera or species, an enumeration of which 
would be too lengthy for this paper. 
We now come to the fact that the ancestors of our Cypris be- 
