192 On Ancient Water-fleas. ett ce ll 
and tubercled by deep transverse furrows. The amount of sulcation 
varies very much. Some unisulcate allies, formerly termed Beyrichiz 
simplices (before alluded to), of simple outline, and passing into small 
nonsulcate Leperditioid forms, have been separated as Primitiz. The 
Beyrichiz proper (B. jugosx) have the surface of the valve impressed 
with two or three strong vertical furrows, extending from the back 
to the ventral portion of the valve, and dividing the surface into 
three or more unsymmetrical lobes, transverse ridges, or bosses, 
which vary considerably in size, mode of subdivision, and relative 
position in different species, and to some extent in different stages 
of growth of individuals. The anterior, inferior, and posterior 
margins of each valve are turned sharply inwards, the angle so made 
bemg marked externally by a prominent ledge, either slightly 
rounded or trenchant (and sometimes spiny), forming a narrow 
compressed border along these three edges of the external surface of 
the valve. These edges of the valves close together by the marginal 
flange of the one valve being received within that of the other. 
The valves are almost equal in size, the ventral edge of the left 
valve very slightly overlapping that of the right. The surface is fre- 
quently marked with pittings, pimples, or other ornament. In some 
species (B. Kloedeni, B. tuberculata, B. Buchiana, and B. impen- 
dens) the antero-ventral lobe has been found to be enormously dis- 
tended iti old specimens.* 
One group of the Beyrichix, typified by B. Wilckensiana (Fig. 
19) and its variety plicata, are recognized as the Corrugatez. 
They have the surface of the valve convex, impressed with two ver- 
tical furrows, not reaching across the valve, but marking out three 
unequal gibbous lobes. There is also a third, smaller furrow, 
defining a narrow semilune at the anterior end of the valve; and 
indeed there are two’ such small parallel vertical furrows in the 
variety (or species ?) plicata. 
There are thirty-nine recorded species of Beyrichia from the 
Silurian, only two from the Devonian, and seven from the Carbon- 
iferous strata. 
5. In Kirkbya (Fig. 15) the carapace-valves are flattish, thick, 
oblong, impressed with a subcentral pit, and raised into ridges, some 
concentric with the margin, associated sometimes with longitudinal 
riblets or wrinkles, and often accompanied by a reticulate ornament. 
In shape the valves are suboblong, usually higher behind than be- 
fore ; the extremities are more or less rounded, but one often much 
more obliquely than the other ; the dorsal border is straight, and 
its ends are subacute; the ventral border is nearly straight in its 
middle third, and boldly curved at the ends; the hinge is simple. 
The ventral edge of the dextral valve overlaps slightly that of the 
other. The subcentral pit or sulcus is sometimes above and some- 
* Jones, ‘Pal. Biy. Entom.,” Geol. Assoc. Proc., 1869. 
