CARBONIFEROUS BRACIIIOPODA. 
293 
Manchester Geological Society/ vol. i, p. 224, 1841), he describes under the name 
Spirifer filiaria. Brown (see his pi. vii, figs. 62 — 63) a valve of Orthis Michelini, which he 
states to have been found at Settle, in Yorkshire, and where we know the shell to be common. 
Capt. Brown's name will require to be added to the synonyms of L'Eveille's species.^ 
In p. 36 of my Introduction, Dr. Carpenter observes that " the prevalent character in 
the genus Orthis is that of perforation, which presents itself in the following species : 
biloba, canalis, elegantula, filiaria, hybrida Michelini, resupinata, striatula, testudinaria. 
Of nearly all these it is particularly noticeable that the openings of the perforations on 
the external surface of the shell are arranged in regular rows on the ridges of the plica- 
tions." 
In my description of Orthis Michelini, at p. 133 of my ' Carboniferous Monograph,' I 
said, " Intimate shell-structure perforated by small canals, of which the external orifices 
under the shape of punctures cover the entire surface of the valves I also observed that 
the larger pores are the bases of broken spines. 
Subsequent to the publication of my description, and quite recently, Mr. John 
Young, of the Hunterian Museum, Glasgow, has devoted considerable attention to the 
pores observable on the outer and inner surface of the valves of this species, and this 
has resulted in the discovery of three different series of pores on the external surface of 
the valves. First, a series of very numerous and minute microscopic perforations that 
reach the inner surface of the shell, and which incline to arrange themselves in rows on 
the ribs of the shell, leaving lines free of pores between them. This first series travers- 
ing the thickness of the shell is distinctly seen on its inner surface. These minute per- 
forations have been ascertained by Mr. Young to be quite as numerous on the inner 
surface as on the outer, and moreover to be in relative numbers almost, if not quite, 
ten times as numerous as those of the second series. A second series of pores, larger 
and less numerous than those of the first series, is present ; and a third series which, 
at least twenty times larger and stronger than those of the second series, belongs to 
the bases of the larger broken spines. After much research and consideration, Mr. 
Young has arrived at the conclusion that in all probabihty the second series of pores are 
the bases of much smaller tubular spines, that once covered the surface of the shell, but 
were too delicate for preservation on the surface of the shells as we now find them. Mr. 
Young has also ascertained that the pores of the second and third series, referable to the 
spines, only enter in a slanting direction for a little distance into the substance of the 
shell. He proved this by two methods. First, by filing down the surface of the shell 
with a very fine flat file and polishing the surface afterwards with a fine honestone ; 
1 la the same paper Captain Brown describes and figures another Bracliiopod under the name of 
Spiriftv Gloveri (pi. vii, figs. GO and 61, of his Memoir). The figure does not, however, indicate a 
specimen referable to that genus, and all my efforts to obtain a sight of his type have failed. Professor 
Boyd Dawkins informs me that the shell was in the collection of a Mr. Gibson, whose specimens have 
been hopelessly scattered. 
