Paleozoic Bivalved Entomostraca. 359 
Of the two Entomostracan casts (internal moulds) the 
shorter form has a squarish Leperditioid outline, with a cen- 
tro-dorsal depression (fig. 1 @) and a marginal rim and furrow 
along the ventral border (fig. 16). The surface of the cast 
is smooth, and its convexity is greatest in the posterior half 
(fig. 1 6). The other specimen has these features modified 
by the pressure which has affected it crosswise from ventral 
to dorsal region. . 
It is usually difficult to determine the species of Primitive 
(see ‘ Monograph Silur. Fossils of Girvan,’ by Nicholson and 
Etheridge, fasc. ii. 1880, p. 221), and hazardous to attempt 
the specific allocation of their shell-less casts. At first sight 
this Primitia has much resemblance to P. prunella, Barrande 
(Syst. Silur. Bohéme, vol. i. Suppl. p. 550, pl. xxvi. figs. 5 
and 6), and to P. Fischert, Gihlert (Bull. Soc. Géol. France, 
ser. 3, vol. v. p. 584, pl. ix. fig. 5); but its edge view (fig. L 
6) gives a different profile, and, instead of being symmetrically 
and gently convex, is much elevated or swollen behind and 
depressed in front, like that of P. Barrandiana (not well 
drawn in fig. 11, e, pl. xv. ‘ Girvan Fossils,’ 1880). Indeed 
the valve of the variety of P. Barrandiana shown in fig. 11 
¢ (op. cit.) approximates very closely in form to the cast before 
us (fig. 1.a). The latter, however, has not so deep a dorsal 
sulcus as some internal casts of P. Barrandiana from Girvan 
exhibit. 
To refer our Carboniferous Primitia from Devon to a 
Lower-Silurian species may be regarded as bold and hete- 
rodox; but some Ostracodous Entomostraca (so far as valves 
bear evidence) are already known to range from the Silurian 
to the Carboniferous system (for example, Beyrichia inter- 
media, see Ann. & Mag. Nat. Hist. ser. 4, vol. xv. p. 55), 
and others from Silurian and Carboniferous strata appear 
to be undistinguishable (see Geol. Mag. dec. 2, vol. viii. 
. TA). 
A very fine Leperditioid Primitza is known from the Lower- 
Carboniferous strata of Brunton, near Chollerford, in North- 
umberland, namely P. Tater, Jones (described as a Beyrichia 
in 1863, see Proc. Berwicksh. Naturalists’ Club for 1864, 
p- 88, fig. 3). Its more ovate outline and more symmetrical 
and central convexity distinguish it from the Devonshire 
species; and its very Leperditia-like shape, its neatly defined 
dorsal sulcus, and its acutely ovate edge view separate it from 
the other Primitie mentioned above. 
Doubtless all these Primitie were closely related, however 
wide apart their habitats and however long the period through 
which they existed. Their exact points and degrees of rela- 
