78 PERMIAN FOSSILS. 



smaller vessels), in Strophomena alternata} Atrypa reticularis^ Orthisina Verneuili^ and 

 Leptana analoga (PL XX, fig. If). 



Many palaeontologists 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 

 in 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 Craniadce 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 turbinatm (PI. XX, fig. 9 a), 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 

 Leptana 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 



' Davidson, Mem. sur les Brach. ; Bull, de la Soc. GeoL, 2"" serie, t. v, pi. iv, fig. 1 b. 

 2 Op. cit., pi. iii, fig. 35. 

 ^ Geology of Russia, vol. ii, pi. xii, fig. 1 h. 



* Probably it \?a8 the differences here indicated vrhich led Goldfuss and others erroneously to conclude 

 the impressions of Crania to be the production of the labial appendages. 



