78 PERMIAN FOSSILS. 
smaller vessels), in Strophomena alternata, Atrypa reticularis,” Orthisina Vernewil, and 
Leptena analoga (P\. XX, fig. 7/). 
Many paleontologists suppose the reniform lobes to be due to the labial appendages. 
One very strong argument, however, against their being considered in this light, is 
in the fact that labial appendages are not pallial organs: they are parts existing 
independently of, and between, the lobes of the mantle. Now the organs that have 
produced the reniform impressions it is difficult to conceive to have pertained to 
anything else but the mantle ; in short, to have been otherwise than true pallial organs. 
Originating as they undoubtedly do in the same place as the primary vascular trunks 
im the fossils just named, that is, between the scars of the divided extremities of the 
valvular muscles, is both a direct and conclusive evidence in favour of this view; 
and it may be said to be still further supported by the fact next to be brought 
forward. 
In both valves of the family Craniade@ there are two large dilated impressions, either 
in relievo or intaglio, passing singly out from between two muscular scars situated on 
each side of the median line, and in their course following the anterior curvature of 
the shell, and terminating at a little distance short of the centre of its anterior half. 
These impressions vary in form in different species. In Crania costata they are simple, 
as in the above description; while in Criopus turbinatus (Pl. XX, fig. 9a), and some 
others, they become digitated on the outside; in all known species, however, the 
main features of these impressions are, their originating between the lateral muscular 
scars, their sweeping round to the front of the shell, and their dilated form—features 
closely identifying them with the reniform lobes of Productus. 
Comparing the slender, complex, ramified, vascular markings of Camerophoria and 
Leptena with the dilated and simple impressions of Crania costata, there seems room 
to warrant their advocated homology being demurred to until some other evidences 
are adduced.* 
When either valve of Criopus anomalus is examined, it is seen exhibiting a pair of 
digitated impressions similar in form to those of C. turbinatus ; and on examining the 
animal of the same shell, each lobe of the mantle is observed to be furnished with two 
vascular structures of a perfectly corresponding form, and crowded either with the 
ovaries or testes, clearly proving that the former have been caused by the pressure of 
vessels loaded with the reproductive organs. Coupling this fact with the similarity 
both of form and origin of the reniform lobes of Productus with the impressions of 
Crania, particularly those of C. costata, and considering the conclusion already arrived 
1 Davidson, Mém. sur les Brach. ; Bull. dela Soc. Géol., 2™° série, t. v, pl. iv, fig. 1 6. 
2 Op. cit., pl. mi, fig. 35. 
3 Geology of Russia, vol. 1, pl. xu, fig. 1 6. 
4 Probably it was the differences here indicated which led Goldfuss and others erroneously to conclude 
the impressions of Crania to be the production of the labial appendages. 
