180 Sciehtific Riviem. 



scure points, respecting which authors had fallen into error. Va- 

 rious important changes have been made in the nomenclature. A 

 more detailed description has been given of the anatomy of the ani- 

 mals of Lamarck's family of the Naiades. Eighteen new species 

 of U?iio, and four of Symphynota have been described. The latter 

 genus has been instituted by Mr. Lea for the reception of all the 

 fresh water connate shells, at present distributed among various 

 genera, viz. Hyria of Lamarck, Dipsceas of Leach, and Cristaria, 

 Prisodon, and Paxyodon of Schumacher. 



There cannot be a better method of clearing up the confusion 

 which often prevails among species, than the consideration of iso- 

 lated genera ; for in the minute investigation of species which re-, 

 suits, many distinct facts will naturally present themselves, which 

 would otherwise have escaped unnoticed. 



In the progressive motion, and the description of the parts of the 

 shell founded upon it, Mr. Lea follows the Cuvierian method, 

 which is the reverse of Lamarck's, and in his measurement has 

 adopted the plan of Barnes, the greatest transverse line of the shell 

 being its breadth, the greatest line perpendicular to this the length, 

 and the greatest line from the most ventricose part of one valve to 

 that of the other being the diameter. We have thus the greatest 

 measurements of the shell, and the marginal descriptions give the 

 form. 



He considers the food of the animal to consist exclusively of ani- 

 malcules, having kept several individuals, during a period of ten 

 months, in a basin, without any other food than such as might be 

 afforded by change of water. The animal, he says, is hermaphro- 

 dite ; and in the dissection of an Anodonta undulaia, nearly three 

 inches long, he found the oviducts charged with about 600,000 

 (as nearly as he could calculate) young shells, perfectly formed, 

 both valves being distinctly visible with the microscope. 



" It has been matter of speculation," he says, " how the calca- 

 reous matter was secreted to increase the anterior margin of the 

 teeth, as well as the whole surface. In this examination we found 

 the surface of the broad teeth, some of which were near half an 

 inch thick, to be completely covered with a prolongation of the 

 mantle, extending from the great anterior to the great posterior 

 cicatrix ; so that to have the teeth closed they completely envelop- 

 ed it. This part of the mantle is exceedingly thin and transpa- 

 rent." 



He considers the rays on the outer surface of the epidermis as of 

 no use in specific distinction, most young shells being rayed, while 

 many adults of the same species have none of these markings. The 

 colour he also considers a deceptive character, in which we entirely 

 agree with him. 



IMuch reliance, he says, cannot be placed on the teeth of the 

 Unios, as affording specific characters, unless other parts are at the 

 i?ame time taken into consideration. This we have found to be the 

 case in the feAv British species of the genus, the most puzzling dif- 

 ferences arising from difference of locality. 



