EERA TUM. 



Vol, II., pages 134 and 138. The reader will kindly delete 

 " Platysomidse " from the list of sub-orders of Ganoids, and place 

 these fishes next after the Paleeoniscidae as afnmilj of Lepidosteidfe. 

 The author regrets that, having had only a hurried glance over the 

 ]Droof-sheets of his friend's paper on the Platysoniidfe, he has, 

 tlirough inadvertence, made the erroneous statement (p. 138, foot- 

 note), that the elevation of the Platysomidae to the rank of a 

 distinct sub-division of Ganoids is in accordance with the views 

 of Dr Traquair. On the contrary, Dr Traquak holds that the 

 Platysomidae constitute a family, very distinct from the Pycno- 

 dontidaj, but closely allied to the Palseoniscidse, and that the 

 position of both Palaeoniscidse and Platysomidge is rather in the 

 sub-order Acipenseroidei. 



In their habits the Gasteropods show great differences, 

 most of them being free and locomotive, though some are 

 sedentary. The typical forms move about more or less 

 actively by the successive contractions and expansions of a 

 muscular organ developed upon the ventral surface of the 

 body and known as the " foot." In many cases the posterior 



VOL. II. A 



