ON BRACHIOPODA. 4.23 
external edge is furnished with flatted, triangular, and flexible 
filaments, longer in the middle, and diminishing as they ap- 
proach more to each extremity. Thus each branchial mass 
forms in reality two planes placed one above the other, and 
which, commencing at the mouth, finish very probably at the 
anus. ‘These singular organs are very firm and solid, and 
probably capable, by their movements, of partly opening the 
shell, and coming out to a certain extent, not, however, in the 
way of arms, which the animal would agitate externally to 
attract the water for the purposes of nutrition and respiration. 
The muscular apparatus of the terebratulz is not less re- 
markable than their respiratory system. All the muscles sur- 
round the visceral mass. Some even appear to belong to it, 
and it is in their interstices that the intestines are situated, 
while the largest proceed from one valve to another. Pallas 
describes three pairs, but M. de Blainville could distinguish 
clearly only two. The first, or most considerable, proceeds 
from the bottom of the most convex valve, and is inserted 
near the middle of the anterior edge of the flatted valve. The 
other two, conical, proceed obliquely into the sinus of the 
former. They are very probably the fibres of one of the more 
internal muscles, which issue forth through the orifice of the 
pierced valve, or rather attach themselves to the membrane 
which closes its orifice; for it seems probable that the ad- 
herence of the terebratule takes place by means of this mem- 
brane, and not immediately through the muscular fibres. 
We may observe, that, though the anatomy of these animals 
is not completely known, yet, from all that we have now said 
touching their organization, they seem to hold an intermediate 
place between the lingula and the ordinary bivalves, perhaps 
nearer to the latter. In fact, the gills are certainly not attached 
to the mantle, and the mouth is not provided with extensible 
labial appendages, as in the former ; but also, the gills are not 
distinct from the labial appendages, and are, moreover, solid, 
