lU 
TUE GEOLOGIST. 
young ; but this of course must remain, for the present at least, one 
of those uncertainties with which the science of Palteontology abounds ; 
and I can quite concur with Mr. Toulmin Smith as to the necessity of 
carefully considering what we give out as facts ; for indeed the word 
** certain" has been more often made use of where that of " probable" 
would have been more properly wi'itten. 
In conclusion, whether it be desirable to retain some or all of the 
denominations or subdivisions in the Productida^, no doubt can exist 
as to their intimate relationship. 
Producta is supposed to have been always deprived of hinge-teeth 
and sockets for the articulation of the valves ; and although this is 
the condition in all species hitherto examined, there may possibly have 
existed some exceptions. No distinct area is visible in the generality 
of species, but in certain specimens it is known to exist. Aulosteges 
has been considered by some as a synonym of Strophalosia, but the 
■want of hinge-teeth and the great similarity of its interior details 
■with those of Producta, makes me consider it even more closely con- 
nected with the last-named genus than with that of Professor King ; 
or, in other words, that it is the connecting link between them. 
Strophalosia and Chonetes are distinguishable from Producta by the 
invariable presence of hinge-teeth and sockets, as also by a distinct 
area in either valve, and by other minor interior details. Strophalosia 
was fixed by a portion of its larger valve, while Chonetes was probably 
free, and is in general recognizable by the position and disposition of 
its cardinal spines.'* 
In Notes No. 3 -we will endeavour to describe and illustrate the 
character of the Strophomenidce. 
* Those who may feel desirous for more amjile iiifoniiation concerning the 
Productidffi, will do well to consult Prof, de Koninck's excellent " Monograpliie 
des Genres Productus et Chonetes, Liege, 1847 ;" also the second volume of the 
" Geology of Russia, in Europe and the Ural" (1845) ; Count Keyserling's 
" Petsclioraland " (1846) ; King's " Monogi'aph of the Permian Fossils of 
England" (1850) ; Sowerby's " Mineral Concholugy ;" Woodward's " Manual of 
the ]\Iollusca," and various other works and papers by MM. de Verneuil, Geinitz, 
Kutorga, Martin, and Howse, as well as the three editions of my " General 
Introduction," &c. In my "Monograph of British -Permian Brachiopoda," pub- 
lished in 1858, the subject has also been attentively re-examined ; and it may not 
here perhaps he considered out of place for me to remark, that during the careful 
preparation of that work, which occupied the greater portion of my time during 
one year and a half, I did my very utmost to be just and fair towards all con- 
cerned, allowing no bias or preference to interfere with my judgment ; and 
although I may be mistaken with respect to certain scientific questions, I have 
not hitherto perceived any valid grounds for altering the conclusions tlierein 
expressed. 
