Dr. J. B. Gray on some Families of Bivalve Shells. 35 



the species. This is an advantage when only a single genus of a 

 family, or only a single or a few species of a genus, are described ; 

 but, in a work on all the species of a family, if each kind was so 

 described and characterized, whose life would be long enough to 

 read and identify the animal now known in the different Museums? 

 Mr. William MacLeay has well observed, " The modern art of 

 describing is too long, often insuperably long, while human life 

 remains as short as ever." (Illus. Zool. South Africa, 54.) The 

 system of long descriptions is not required, when all, or even the 

 greater number of the species of a family or genus has been per- 

 sonally examined, and especially when they, or the greater part of 

 them, are present at the same time before the eyes of the author, 

 as is the case with most families of animals in the British Mu§eum. 

 Then the characters which divide them into smaller groups, and 

 these groups again into genera, soon present themselves to the 

 student, and the characters thus discovered are as easily arranged 

 in a tabulated form. Hence, that which would be very difficult, 

 indeed almost impossible for a person to do with a small collec- 

 tion, or only with the descriptions of others before him, becomes 

 comparatively easy to one who has a large and well-arranged col- 

 lection at his command, and with common care, the short com- 

 parative descriptions of a naturalist with such advantages are 

 and ought to be very superior to the long characters and detailed 

 descriptions of one who has only a few specimens, or the descrip- 

 tions given in books, for comparison. 



The value of both the short character and the long description 

 must depend on the accui'acy and observant faculties of the de- 

 scriber ; but there is less liability to error in the short character 

 than in the long description ; for to make the former, the author 

 must submit the species to an accurate examination and rigid com- 

 parison, which must draw his attention to those parts of the animal 

 or shell which are least liable to vary, and hence afford the best 

 character to separate the species ; while the describer of an indi- 

 vidual specimen, who is likely only to be attracted by the more 

 prominent peculiarities of the species, may overlook the most cha- 

 racteristic particular. This is well illustrated in M. F. Cuvier's 

 work on Mammalia, where every individual has at least one, and 

 often three or four pages of description, and in the most, the cha- 

 racter which distinguishes it from its congener, if there is any 

 other species of the genus, is not given. Again, in Schonherr's 

 work on Curculionidoe, in which seven large volumes of close type 

 are filled with the descriptions of the species of the Linnaean genus 

 Curculio, each species occupies a page or more ; and at the end 

 of the description the reader is informed that such a species is very 

 distinct from a certain other one, as will be seen by the descrip- 

 tion ; yet, when the descriptions are compared word by word with 



3* 



