DAVIDSON — rAL^ONTOLOGICAL NOTES ON THE BRACHIOPODA. 105 
The external sui-face varies according to the species. In some it is 
almost smooth ; in others it was longitudinally and finely striated, or 
coarsely costatcd, as well as intersected by numerous concentric 
wrinkles, or lines of gi'owth. All the specimens appear to have been 
furnished, more or less, with tubular spines. In some Pr-oducfa, 
Strophalosia, and Aulosteges, hoiXi valves were so ornamented; while 
in others they were restricted to the ventral valve. In certain species 
they are small, delicate, and so closely packed as to conceal every por- 
tion of the shell, with the exception of the area ; while in others they 
were irregularly scattered, and chiefly confined to the auriculate 
portions of the valves. In certain species the spines exceeded by four 
or five times the length of the shell ; and while some were almost as 
delicate as the hair of one's head, others exceeded a line in diameter ; 
the dimensions of the shell, however, had nothing to do with that of 
the sj^ines ; for in some small species these wei'e few and large, while 
the revei'se has occasionally been found to be the case with species of 
the largest dimensions. Chonetes alone appears to have differed from 
Producta, Atdosteges, and Strophalosia, in its tubular spines, which are 
in all known species confined to the cardinal edge of the ventral 
valve, where they are regularly disposed and interspereed, generally 
increasing in length as they approach the extremities of the shell. 
The intimate structure of the shell has been described by Dr. Car- 
penter, in the second chapter of the " General Introduction " to my 
work on British Fossil Brachiopoda, and from which I will extract the 
following passage :— " In all the genera of this family large perfora- 
tions exist, resembling those of Stroplwiriena depressa in their general 
aspect, and in the infundibular arrangement of the laminae of the shell 
around them. Where the shell is furnished with spines, as is especially 
the case with Producta horrida, the perforations are continued 
into them ; and such passages are of more than the average 
dimensions." 
These are the more important external features presented by the 
family. We will now examine the interior' dispositions, and will com- 
mence with those which relate to the smaller or dorsal valve. 
In the Produdidce the internal surface of this valve is more or less 
convex, and presents in the middle of the hinge-line a prominent 
bi-lobed or tri-lobed projection, which has been termed a " cardinal 
