CARBONIFEROUS BRACHIOPODA. 
301 
" 17. Productus cardonarim,aiLid 18. Frod. Griffitldanus. — I have no Scotch specimens 
of these beside me, and cannot, therefore;, speak of their perforations. The two examples 
of the latter species sent me from Belgium are too much mineralised to show structure ; and 
the same is the case with one or two other Produdi from Ireland in our collection." 
Prof. W. King, D.Sc, has likewise kindly favoured me with the following obser- 
vations : 
" De Koninck's specimen of Productus semireticulatus, which you sent me for exami- 
nation, is undoubtedly perforated, but in it this character assumes a form somewhat 
different from that common to the perforations of a great many Palliobranchs. It is* 
however, in unison with the general perforate system of these shells, 
" I have closely examined some species closely allied to Productus semireticulatus, viz. 
Prod, punctatus, pustulosus, and scabriculus^ and find that they all agree in having their 
valves perforated. Some specimens, both from Redesdale and near Galway, are wonder- 
fully well preserved, but in no case have I yet been able to trace the perforations passing 
externally through the valves. In some cases the outermost layer is translucent, and one 
can easily see the perforations coming close up to it ; but, although there are occasionally 
appearances to the contrary, I have never been able to satisfy myself that the distal 
extremity has actually penetrated into this layer. 
" On referring to ray Memoir " On the Histology of the Test of the class Pallio- 
branchiata" ('Trans, of the Royal Academy of Ireland,' vol. xxiv, part 1, pp. 439 — 
455, 1868), it will be seen that I have cited Carpenter and Quekett, as supplying 
evidence that the perforations in the shells of the Terehratulidce answer to the csecal 
appendages of the mantle or pallium of the animal, each perforation being occupied by 
one of the latter. 
" According to these authorities the csecal appendages originate on the outer mem- 
brane of the pallial lobes, and have their distal extremity more or less flattened or disc- 
shaped, and encircled with a fringe of ' exceedingly minute radiating lines or membranous 
filaments.' It would also appear that both considered the orifices of each perforation in 
the shell-substance to be closed by a 'disc-shaped body' — 'membranous discs' — ' dis- 
coidal opercula,' that the filaments served the purpose of ' a fringe of cilia ' disposed to 
produce currents of water over the extremities of the caeca, and thus subserve respiration. 
It turned out, however, that the observations which I made while preparing my memoir 
did not confirm these views. 
" In well-preserved specimens of different species of Terebratula, Wcddheimia, Tere- 
bratidina. Crania, and other genera, I found nothing more than the common epidermis 
passing uninterruptedly over perforations, in this way closing their ends — the distal 
extremities of the caca abutting against the under side of the epidermis — the frhige of 
filaments, which varies much in different species, radiating variously from the csecal 
extremities, and, though evidently penetrating the surrounding portion of the shell, 
never being seen to pass into or through the epidermis. 
