116 PERMIAN FOSSILS. 
Hypothyris, at least, taking as an example H. acuminata, in which the vessels, as 
exhibited on casts, have been distributed over the mantle pretty much the same as in 
Camarophoria multiplicata (vide Pl. VIII, figs. 6, 7). The veins (2) and the arteries (4), 
which the former are occasionally seen to inclose on sharp casts, have been similarly 
disposed on both lobes of the mantle. In each valve there are two main trunks, which 
first make their appearance at the anterior end, and on each side of the medio- 
longitudinal plates (7); but evidently, from their impressions occasionally being seen 
running down each side of the plates, originating within or near the arch-shaped 
process of the one valve, and the spatula-shaped process of the other: they run forward 
for a short distance, then sweep round towards the cardinal region, and finally run 
forward again to nearly their origin, forming in this way two small, nearly complete 
circles, each of which is limited to the lateral half of the central region of the valves. 
In their circuit, the main trunks give off at regular distances on their outside several 
branches, each one of those in front and on the sides becoming thrice divided in its 
progress to the margin of the valves: near the margin of the mantle, these branches, 
it is probable, were more minutely subdivided. 
I have never seen any of the vessels enlarged so as to induce the belief that they 
were ever charged with the genital organs, as is the case in certain Terebratulide ; but 
from certain impressions which are occasionally observed within the vascular circles 
above described, and immediately adjoining the medio-longitudinal plates, I am 
led to believe that the latter were the seats of reproduction. Hach of the main 
trunks of Hypothyris acuminata forms an ellipse, in the inside of which, but outside 
of the muscular scars, there are often seen similar genital-like impressions; and I 
consider the large lateral circles, circumscribed by a main trunk in the valves of 
Leptena analoga (vide Pl. XX, figs. 6,7), to be the localities of the reproductive 
organs. 
In Camarophoria, when the shell has attained a proper size, its margins, 
instead of meeting each other, are acutely eflected, or, in other terms, they strike 
off horizontally, and continue to grow in this direction, so that the shell becomes 
furnished with two wide marginal expansions running out in a horizontal direction, 
and parallel to each other (vide Pl. VI, figs. 20, 21; Pl. VIII, fig. 8). In the 
specimen, represented in fig. 8, Pl. VIII, the marginal expansions exhibit some 
vascular impressions; but they do not display any appearance of the vessels being 
minutely divided. The lamellee of certain Bivalves (e. g. Venus lamellata, Lam., also 
certain Oysters) and Palliobranchs (e. g. Discina ostreoides, Cleothyris (Atrypa) plano- 
sulcata, J. de C. Sow., &c.) appear to be the same as the marginal expansions ; but there 
is this difference,—the latter are only developed once, and when the shell attains a 
certain size, whereas in the former they are repeatedly developed during all stages of 
the shell’s growth. It would therefore appear that nothing of the precise kind occurs 
in other shells, unless it be, as I strongly suspect is the case, the geniculated portions 
