116 PERMIAN FOSSILS. 



Hppothyris, 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 muUipUcata (vide PI. VIII, figs. 6, 7). The veins («') and the arteries [J), 

 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 (/) ; 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 Terehratulidce ; 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. Each 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 

 LeptcBna analoga (vide PI. 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 efiected, 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 PI. VII, figs. 20, 21 ; PI. VIII, fig. 8). In the 

 specimen, represented in fig. 8, PI. VIII, the marginal expansions exhibit some 

 vascular impressions ; but they do not display any appearance of the vessels being 

 minutely divided. The lamellae 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 groAvth. 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 



