On the Affinities of the Onchidia. 259 



it, to say the least, no support, but rather are deemed by one 

 competent to judge to be decidedly adverse to what is here 

 claimed. 



The palgeontological contradiction shown in the plants and 

 animals of the Fairplay beds is not unknown to American 

 geology, as every one is aware ; but I do not know that it has 

 been pointed out in this country at this horizon or in this 

 direction — the discordance appearing later in time and the 

 plants indicating a younger and not an earlier age than the 

 animals. An exactly parallel case appears to be shown in 

 Eastern Russia, for in discussing the poorer strata of Kar- 

 galinsk, which he refers to the Permian, Twelvetrees says, 

 " As regards the flora [eleven species] the list has a Paleeozoic 

 aspect, but a Secondary one as respects the reptilian remains" 

 [four species cited]*. 



Exploration of the locality will continue, and it is hoped 

 that future material may throw more light upon the question. 

 It may, however, be added that the few other insects found 

 appear to have no Palseozoic relations whatever. 



XXXIL — On the A-ffinities of the Onchidia. 

 By Dr. K. BEEGHf. 



The remarkable group of marine or amphibious Ichnopod 

 Mollusca which has long been known under the name of 

 Onchidiurti has often given rise to scientific controversies, which 

 of late years have also had relation to the affinities of these 

 animals, and consequently to their position in the system. 



In their external characters these animals strongly resemble 

 the Doridaj ; like these they are also marine or amphibious, 

 and they belong, like the Doridse, chiefly to the Indo-Pacific 

 marine regions. When closely examined as to their internal 

 structure, however, the Onchidia, notwithstanding tlie 

 " opisthobranchiate " position of the heart, prove to be very 

 different from the Doridse, and rather agree with the Pulmo- 

 nata, even to the extent of being furnished with lungs. For 

 this reason, although Blainville placed the Onchidia [Peronice) 

 near the Doridaa in the group Nudibranchiata, most inves- 

 tigators and systematists since Cuvier and Ferussac have re- 

 ferred them to the Pulmonata. 



Very recently, as already mentioned, a very interesting 



* Quart. Journ. Cleol. Soc. Lond. xxxviii. p. 495. 

 t Translated from the ' Moi-phologisches J.ihrbuch,' Band x. pp. 172- 

 181. 



20* 



