100 
THE GEOLOGIST. 
my endeavour to make this article as explicit and intelligible as 
the subject will permit ; for in palieontology 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 Strophomenid^ [Orthidce of some authors) and 
PaoDUCTiDiE have been the subject of long and patient research; and, 
although much progress has been made towards their elucidation, 
t am not yet entirely satisfied that the differential characters 
specified by authors are in every case of sufficient importance or 
value to wari'ant 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, Strophomence, and 
Frodiictoe ; but since the days of Dalman, Eafinesque, 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 ; * 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 differences 
observed are constant and of more than specific importance. 
* 111 the last page of the German edition of my " General Introduction " 
(Vienna, 1856), Professor Suess has appended a list of no less than 160 generic 
names, under which the known species of Brachiopoda had been located up to the 
year 1856 ! And since that period, several others have been jiroposed by Messrs. 
Hall, Suess, and Billings. In the French edition of the same work, I provision- 
ally admitted 24 genera and 22 sub-genera, making a total of 46 ; but of these, 
a few were mentioned with doubt ; and, although I Ijelieve we are working in the 
right path, much care must be exercised not to exaggerate the number of genera 
and sub-genera, and tluis to be causing confusion where simplicity should prevail. 
