100 



THE GEOLOGIST. 



my endeavour to make this article aa explicit and intelligible as 

 the subject will permit ; for in palaeontology it is not always possible 

 to avoid having recourse to certain technicalities when one is desirous 

 of conveying precise information upon special subjects. The reader 

 •will, however, experience but little difficulty, if he will cast his eye 

 over the accompanying figures, which have been drawn with all 

 possible accuracy, so as to make up for any deficiencies that may 

 exist in the descriptions. 



The families . Steophomenid^ {Orthidce of some authors) and 

 Productid^ have been the subject of long and patient research; and, 

 although much progress has been made towards their elucidation, 

 I am not yet entirely satisfied that the differential characters 

 specified by authors are in every case of sufficient importance or 

 value to warrant the many divisions at present provisionally esta- 

 blished. 



Every geologist and the generality of collectors are acquainted 

 with the external shape of some species of Orthis, StrophomeiKB, and 

 Productce ; but since the days of Dalman, Rafinesque, and James 

 Sowerby, these old genera have been much subdivided, and others 

 have been discovered, which, by presenting certain intermediate 

 characters, have proved the natural connexion which exists between 

 the two families. It cannot be expected that palaeontologists, however 

 diligent and learned, should be able all at once to arrive at a just and 

 satisfactory appreciation of the value of certain groups of extinct 

 animals; but what does more injury to science, and retards its pro- 

 gress, is the precipitation with which new genera are sometimes pro- 

 posed j * and it should always be remembered that, although it is 

 necessary and right to separate what is dissimilar, one cannot be 

 too careful and cautious, while determining whether the difierences 

 observed are constant and of more than specific importance. 



* In the last page of the German edition of my "•'General Litroduction " 

 (Vienna, 1856), i^rofcssor Suess has appended a list of no less than 160 generic 

 names, under -which th.e knomi species of Bracliiopoda had heen located up to the 

 year 1856 ! And since that period, several others have been proposed by 3Iessrs. 

 Hall, Suess, and l>il];!igs. In the French edition of the same work, I provision- 

 ally admitted 24 geneia and 2-2 sub-genera, making a total of 46 ; but of these, 

 a few were mentioned with duubt ; and, although Tbelieve we are working in the 

 right path, much care nnist be exercised not to exaggerate the number of genera 

 and sub-genera, and thus to be causing confusion where simplicity should prevail. 



