376 Notices respecting New Books. 



order to present the reader with the natural arrangement. The 

 whole book indeed is printed far too expensively for a local Flora] and 

 the authors probably would have done themselves, as well as the pub- 

 lic, more justice, if they had condensed their matter within a smaller 

 compass. It is the extensive diffusion of science that will do good to 

 the present generation ; and to effect this, the spirit of a book should 

 not be diluted too copiously. 



But after all, we may venture to recommend this work to those 

 lovers of Nature who are resident in Devon, and to the numerous 

 visitors that its romantic and picturesque scenery and genial climate 

 are constantly attracting to its shores. 



Observations on the Genus Unio, together with Descriptions of Eighteen 

 New Species ; and of the Genus Symphynota, now separated from the 

 Family of Naiades, containing Nine Species. Read before the Am. 

 Phil. Soc. November 1827 and March 1829, and published in their 

 Transactions, vol. hi. N.S. By Isaac Lea, M.A.P.S. M.A.N.S. &c. 

 Philadelphia: 1829. 4to, pp. 71. Eight coloured engravings. 



[In the Phil. Mag. and Annals, N.S. vol. iv. p. 372, we gave the 

 characters of six new species of Unio, as described by Mr. Lea in 

 a former paper : we shall now present to our readers the characters 

 of the shells described by this zealous conchologist in the memoir 

 before us, prefacing them with an extract from his introductory 

 remarks relating to the arrangement and groups of the Naiades.'] 



It is the opinion of some eminent conchologists that the family of 

 the Naiades possesses but one genus, and that the genera into which 

 it is at present divided are only species, and the species varieties. 

 Were we to adopt this division, we should be in a worse dilemma 

 than before ; for we can scarcely imagine bivalves more different from 

 each other in form than are some of our trans-AUeghany species of 

 Unio. 



How totally different is the rectus of Lamarck from the irroratus? 

 (nobis). The first is four times the width of its length, whilst the 

 latter is longer than broad. The one is broad rayed, in fine specimens; 

 the other possesses dotted lines universally. The triangularis of 

 Barnes is entirely dissimilar to the nasulus of Say, as is also the 

 circulus, herein described, from the lanceolatus (nobis) ; and the same 

 may be said of plicatus and pictorum. Two species could be scarcely 

 more unlike than the smooth and radiated siliquoideus of Barnes and 

 the beautiful tuberculated lacrymosus (nobis) ; and the same remark 

 may be applied to the cylindricus and alatus of that excellent con- 

 chologist Mr. Say. Many other species could be thus contrasted, 

 but I deem the above sufficient, upon examination, to prove the just- 

 ness of my remarks, and the necessity, in the present state of our 

 knowledge, to retain the species, whatever maybe the changes in the 

 genera*. 7. Unio 



* In a letter addressed to me by William Cooper, Esq., an intelligent 

 naturalist of New York, he says, " There are now, I think, not less than 

 thirty North American species of Unio well established, and perhaps seven 

 or eight more. That they are species, each perpetuating its peculiar form, 



subject 



