200 TtiE katural htstout review. 



" defined characters by whicli to distinguisli them. Tliat we do not 

 " find any limiting boundaries, goes far to prove that there are no 

 " such things as genera in nature, and that what we call so are 

 " neither more nor less than artificial aids to memory and classifica- 

 *' tion. In no family which I have studied have I been more struck 

 ^' with this than in the Nitidularice. The affinities which we find 

 " constantly appearing in unexpected places, and the gradual shading 

 " off" which we see in others, show that the whole group is a perfect 

 *' network of relationship, and that, with a few exceptional breaks, 

 " the boundaries of the genera, or subsections, into which for con- 

 *' venience sake we divide them, have no real existence." 

 Of papers on Mollusca we have three, viz. : — - 



1. AYright — On Naiisitora. 



2. Blanford — On Tanalia, PJiilopotamu and Paludomus, 



3. Hancock — On the Eenal organ in the Nudibranchs, 

 Nausitora is a new sub-generic form, related to Teredo, and is 



worthy of note because of its fresh-water habit, thus diff'ering 

 from all previously known members of its group. The specimens 

 here described were taken from trees which had been immersed in 

 the river Comer, a remote tributary of the Granges. 



Mr. Blanford considers Tanalia and Philopotamis as sub-sections 

 of the old genus Melania. This opinion he demonstrates in the first 

 part of his paper. In the second he describes the Cingalese species 

 of Fhilapotamis and Paliidomus. 



"We have seen that the best Essay in the volume before us was 

 also the first, and discussed a botanical subject. By a curious con- 

 trast, what we must consider the memoir next in order of merit 

 concludes the volume, and is zoological. We refer to Mr. Hancock's 

 paper ' On the Structure and Homologies of the Eenal organ in the 

 Nudibranchiate Mollusca,' of which we hope to ofi"er an analysis in 

 our next number. It would be impossible to give it adequate notice 

 within the brief space remaining at our disposal. 



Of the plates which accompany this volume we have said but 

 little. All its memoirs are illustrated, those on Botany, with few 

 exceptions, by Fitch. Excellent, also, are the illustrations appended 

 to the papers of Mr. Murray and Mr. Hancock, though differing as 

 much in style as in subject matter from one another. 



In truth it is a pleasing task to take up a richly-varied volume 

 like this, and glance, as we have done, through its contents. Thus 

 may the naturalist, putting aside for a time more special studies, 



