DAVIDSON — ON BRITISH CARBONIFEROUS BRACHIOPODA. 
55 
disposed to believe that Sowerby's figures of P. liemisplioeyicus, 
belong to varieties of P. giganteus. This matter vdll be further 
discussed in my monograph, for the limits prescribed to this commu- 
nication will not peiTuit of more lengthened explanations. P. 
liumerosus has been estabhshed on some singular internal casts; 
the shell itself not having been hitherto discovered ; but I cannot 
agree vrith those who would refer these casts to either P. giganteus 
or P. semireticulatus. The prominences in the casts or deep conical 
hollows (in the shell) lor the accommodation of the oral arms indicate 
that the ventral valve was enormously thickened. The position of the 
adductor or occlusor muscle in the ventral valve is also slightly different 
from that common to P. giganteus, and which would of itself, in this 
instance, denote a specific difierence. The material, however; is so 
very imperfect and insufficient that very little can be said upon the 
subject. P. iwohoscicleus, and P. ermineus, P. arcuarms, are new 
species to England, and a very interesting discovery entirely due to 
the indefatigable exertions of my zealous and kind friend, Mr. 
Burrow, who has in the most liberal and generous manner presented 
me with his best, and by me figured specimens. The discovery of 
P. proboscideus, (known in one Belgian locality only,) and of so 
many other species at Settle, in Yorkshire, render that locality 
especially interesting, as it exactly represents with us the equivalent 
of the celebrated locality of Vise, in Belgium. 
P. suh-lcBvis is also a new species to Britain ; but I am not yet 
satisfied regarding the differences said to exist between it and P. 
GliTLstiani ; and should urge a search for more examples of both of 
these large and almost smooth species of Productus. The first has 
been obtained at Leek, in Stafibrdshire, as well as at Llangollen. 
The second is stated by Prof, de Koninck to be from Wales, but of 
which the locality is still unknown. 
P. Wrightii is a small species with fringe, found by Mr. J. Wright, 
at Midleton, near Cork, in Ireland, it differs from P. tessellatus in 
several respects, and both appear good but rare British shells. 
P. Youngianus has appeared to me new ; and in this opinion I am 
supported by Prof, de Koninck, P. carbonarius (if a good species) is 
decidedly very rare, for I have never seen more than two British 
examples wdiich would agree with Prof, de Koninck' s description and 
illustrations of the species. The distinction between P. costatus 
and P. muricatus are also difficult to determine, and I am now 
disposed to beheve that if the last is not a distinct species, it may 
be a good variety of P. costatus. 
Troductiis sinuatus, mider the designation oiLeptmna smtato, appears 
to have been noticed for the first time in England by Prof. M'Coy, 
and. notwithstanding its well defined area, should be located under 
Productus, of which it possesses all the characters, with the exception 
of its well-defined ventral area, a character rare but not impossible 
in the genus Productus ; and I am glad to find that Prof, de Koninck 
entirely coincides -svith the opinions I have expressed upon the subject 
relating to his remarkable species. P. sinuatus has also been recently 
